Add migration guide

Author: djbe

CHANGELOG.md

@@ -4,6 +4,9 @@
 
 ## Master
 
+Due to the removal of legacy code, there are a few breaking changes in this new version that affect both template writers as well as developers. We've provided a migration guide to help you through these changes, which you can find here:
+[Migration Guide for 2.0](https://github.com/SwiftGen/SwiftGenKit/blob/master/Documentation/MigrationGuide.md#swiftgenkit-20-swiftgen-50)
+
 ### Bug Fixes
 
 * Fixed color's hex value rounding error.  
@@ -18,6 +21,7 @@
 * Removed deprecated variables. See [SwiftGenKit#5](https://github.com/SwiftGen/SwiftGenKit/issues/5) for more information.   
   [David Jennes](https://github.com/djbe)
   [#35](https://github.com/SwiftGen/templates/issues/35)
+  [#42](https://github.com/SwiftGen/templates/issues/42)
 
 ### New Features
 

Documentation/MigrationGuide.md

@@ -0,0 +1,45 @@
+## SwiftGenKit 2.0 (SwiftGen 5.0)
+
+### For template writers:
+
+#### Colors
+
+- `enumName`: has been replaced by `param.enumName`, should provide default value.
+- For each `color`:
+  - `rgb` and `rgba`: can be composed from the other components.
+
+#### Fonts
+
+- `enumName`: has been replaced by `param.enumName`, should provide default value.
+- For each `font`:
+  - `fontName`: has been replaced by the `name` property.
+
+#### Images
+
+- `enumName`: has been replaced by `param.enumName`, should provide default value.
+- `images`: just old, `catalogs` contains the structured information.
+
+#### Storyboards
+
+- `extraImports`: replaced by `modules` (https://github.com/AliSoftware/SwiftGen/pull/243)
+- `sceneEnumName`: has been replaced by `param.sceneEnumName`, should provide default value.
+- `segueEnumName`: has been replaced by `param.segueEnumName`, should provide default value.
+- For each `scene`:
+  - `isBaseViewController`: removed. You can replace it with a test for `baseType == "ViewController"`.
+
+#### Strings
+
+- `enumName`: has been replaced by `param.enumName`, should provide default value.
+- `strings` and `structuredStrings`: replaced by `tables` array, where each table has a structured `levels` property.
+- `tableName`: replaced by `tables` array, where each table has a `name` property.
+- for each `level`:
+  - `subenums`: renamed to `children`.
+- for each `string`:
+  - `keytail`: renamed to `name`.
+  - `params` structure with the `names`, `typednames`, `types`, `count` and `declarations` arrays: removed.
+  - These have been replaced by `types` which is an array of types. The previous variables
+ can now be reconstructed using template tags now that Stencil has become more powerful.
+
+### For developers using SwiftGenKit as a dependency:
+
+Previously the parser context generation method (`stencilContext()`) accepted parameters such as `enumName`, this has been removed in favor of the `--param` system. Templates will automatically receive a `param` object with parameters from the CLI invocation, and should provide default values in case no value was present in the invocation.