Modify README.md to include new features and examples for v2

[AleksandrRogov]

Rewrite, fix and add new examples to README.md.

This is a time consuming task and any help is greatly appreciated.

The following tasks are related to this:

• Add Power Apps terminology Add Power Apps terminology to README #143
• Describe What's New in v2 What's New in v2 #146

List of sections to be checked/rewritten:

• Getting Started
• DynamicsWebApi as a Dynamics 365 web resource
• DynamicsWebApi for Node.js
• Configuration
• Configuration Parameters
• Request Examples
• Create a record
• Update a record
• Update a single property value
• Upsert a record
• Delete a record
• Delete a single property value
• Retrieve a record
• Retrieve multiple records
• Change Tracking
• Retrieve All records
• Count
• Count limitation workaround
• Associate
• Associate for a single-valued navigation property
• Disassociate
• Disassociate for a single-valued navigation property
• Fetch XML Request
• Fetch All records
• Execute Web API functions
• Execute Web API actions
• Execute Batch Operations
• Work with Metadata Definitions
• Create Entity
• Retrieve Entity
• Update Entity
• Retrieve Multiple Entities
• Create Attribute
• Retrieve Attribute
• Update Attribute
• Retrieve Multiple Attributes
• Use requests to query Entity and Attribute metadata
• Create Relationship
• Update Relationship
• Delete Relationship
• Retrieve Relationship
• Retrieve Multiple Relationships
• Create Global Option Set
• Update Global Option Set
• Delete Global Option Set
• Retrieve Global Option Set
• Retrieve Multiple Global Option Sets
• Work with File Fields
• Upload file
• Download file
• Delete file
• Retrieve CSDL $metadata document
• Formatted Values and Lookup Properties
• Using Alternate Keys
• Making requests using Entity Logical Names
• Using Proxy
• Using TypeScript Declaration Files
• In Progress / Feature List
• JavaScript Promises
• JavaScript Callbacks <- must be deleted
• Contributions

Needs to be added:

• Features
• Dataverse Search API Implement Dataverse Search API #134
• CSDL $metadata document retrieval examples
• v2 breaking changes Breaking Changes in v2 #135
• v1 to v2 migration guide - this is probably going to go to the wiki v1 to v2 migration guide #147

[AleksandrRogov]

Closing this issue there are separate Issues related to Breaking Changes #135, What's new in v2 #146 and the Migration Guide #147 .
All other readme sections were successfully modified.