Update documentation for uniques (This PR renames classes and instanc…

…es to collections and items in the Uniques pallet in order to follow the commonly accepted NFTs terminology.) (#13322)

* Update documentation for uniques

The documentation was outdated after merge of #11389
Using the widely spread term collections and item instead
of the previous class and instance.

* Update README.md

---------

Co-authored-by: Jegor Sidorenko <5252494+jsidorenko@users.noreply.github.com>
Co-authored-by: Jegor Sidorenko <jegor@parity.io>

frame/uniques/README.md

@@ -4,67 +4,71 @@ A simple, secure module for dealing with non-fungible assets.
 
 ## Overview
 
-The Uniques module provides functionality for asset management of non-fungible asset classes, including:
+The Uniques module provides functionality for non-fungible tokens' management, including:
 
-* Asset Issuance
-* Asset Transfer
-* Asset Destruction
+* Collection Creation
+* Item Minting
+* Item Transfers
+* Item Trading methods
+* Attributes Management
+* Item Burning
 
-To use it in your runtime, you need to implement the assets [`uniques::Config`](https://paritytech.github.io/substrate/master/pallet_uniques/pallet/trait.Config.html).
+To use it in your runtime, you need to implement [`uniques::Config`](https://paritytech.github.io/substrate/master/pallet_uniques/pallet/trait.Config.html).
 
 The supported dispatchable functions are documented in the [`uniques::Call`](https://paritytech.github.io/substrate/master/pallet_uniques/pallet/enum.Call.html) enum.
 
 ### Terminology
 
-* **Asset issuance:** The creation of a new asset instance.
-* **Asset transfer:** The action of transferring an asset instance from one account to another.
-* **Asset burning:** The destruction of an asset instance.
-* **Non-fungible asset:** An asset for which each unit has unique characteristics. There is exactly
-  one instance of such an asset in existence and there is exactly one owning account.
+* **Collection creation:** The creation of a new collection.
+* **Item minting:** The action of creating a new item within a collection.
+* **Item transfer:** The action of sending an item from one account to another.
+* **Item burning:** The destruction of an item.
+* **Non-fungible token (NFT):** An item for which each unit has unique characteristics. There is exactly
+  one instance of such an item in existence and there is exactly one owning account.
 
 ### Goals
 
 The Uniques pallet in Substrate is designed to make the following possible:
 
-* Allow accounts to permissionlessly create asset classes (collections of asset instances).
-* Allow a named (permissioned) account to mint and burn unique assets within a class.
-* Move asset instances between accounts permissionlessly.
-* Allow a named (permissioned) account to freeze and unfreeze unique assets within a
-  class or the entire class.
-* Allow the owner of an asset instance to delegate the ability to transfer the asset to some
+* Allow accounts to permissionlessly create NFT collections.
+* Allow a named (permissioned) account to mint and burn unique items within a collection.
+* Move items between accounts permissionlessly.
+* Allow a named (permissioned) account to freeze and unfreeze unique items within a
+  collection or the entire collection.
+* Allow the owner of an item to delegate the ability to transfer the item to some
   named third-party.
 
 ## Interface
 
 ### Permissionless dispatchables
-* `create`: Create a new asset class by placing a deposit.
-* `transfer`: Transfer an asset instance to a new owner.
-* `redeposit`: Update the deposit amount of an asset instance, potentially freeing funds.
+* `create`: Create a new collection by placing a deposit.
+* `transfer`: Transfer an item to a new owner.
+* `redeposit`: Update the deposit amount of an item, potentially freeing funds.
 * `approve_transfer`: Name a delegate who may authorise a transfer.
 * `cancel_approval`: Revert the effects of a previous `approve_transfer`.
 
 ### Permissioned dispatchables
-* `destroy`: Destroy an asset class.
-* `mint`: Mint a new asset instance within an asset class.
-* `burn`: Burn an asset instance within an asset class.
-* `freeze`: Prevent an individual asset from being transferred.
+* `destroy`: Destroy a collection.
+* `mint`: Mint a new item within a collection.
+* `burn`: Burn an item within a collection.
+* `freeze`: Prevent an individual item from being transferred.
 * `thaw`: Revert the effects of a previous `freeze`.
-* `freeze_class`: Prevent all asset within a class from being transferred.
-* `thaw_class`: Revert the effects of a previous `freeze_class`.
-* `transfer_ownership`: Alter the owner of an asset class, moving all associated deposits.
-* `set_team`: Alter the permissioned accounts of an asset class.
+* `freeze_collection`: Prevent all items within a collection from being transferred.
+* `thaw_collection`: Revert the effects of a previous `freeze_collection`.
+* `transfer_ownership`: Alter the owner of a collection, moving all associated deposits.
+* `set_team`: Alter the permissioned accounts of a collection.
 
 ### Metadata (permissioned) dispatchables
-* `set_attribute`: Set a metadata attribute of an asset instance or class.
-* `clear_attribute`: Remove a metadata attribute of an asset instance or class.
-* `set_metadata`: Set general metadata of an asset instance.
-* `clear_metadata`: Remove general metadata of an asset instance.
-* `set_class_metadata`: Set general metadata of an asset class.
-* `clear_class_metadata`: Remove general metadata of an asset class.
+* `set_attribute`: Set an attribute of an item or collection.
+* `clear_attribute`: Remove an attribute of an item or collection.
+* `set_metadata`: Set general metadata of an item.
+* `clear_metadata`: Remove general metadata of an item.
+* `set_collection_metadata`: Set general metadata of a collection.
+* `clear_collection_metadata`: Remove general metadata of a collection.
 
 ### Force (i.e. governance) dispatchables
-* `force_create`: Create a new asset class.
-* `force_asset_status`: Alter the underlying characteristics of an asset class.
+* `force_create`: Create a new collection.
+* `force_asset_status`: Alter the underlying characteristics of a collection.
 
 Please refer to the [`Call`](https://paritytech.github.io/substrate/master/pallet_uniques/pallet/enum.Call.html) enum
 and its associated variants for documentation on each function.