* Add `getFieldMap` method to retrieve a list of all fields for any given class
* Add `TagsToShortcodeTask` to upgrading guide
Adding after the file migration part as this is where it makes the most sense to run it.
* `getFieldMap` accepts an array
* Move to `DataObjectSchema`
* Add `HTMLVarchar` to documentation
Minor refactoring
* Add test for checking that `subclassesfor` works without the base class
Add test `DataObjectSchema::getFieldMap` returns the correct array
* Remove cms dependency
API Add HasRequestHandler interface
API Refactor Link() and url handling behaviour from Controller into RequestHandler
API RequestHandler classes now must define url_segment to have a default Link()
API Clean up redirectBack()
