Improvements to Pluggable Custom Tags #154 

Question:
* Do we need 'InLineTransformerExtension' class? I don't see any place where it is using.

Done:
* Don't use 'ns' as namespace name, let's use 'dg' in all examples.
* Change 'range' to 'set' property name. Let's use 'range' to range. I'll implement it
* Let's use 'dg:assign' tag name instead of 'dg:set'. It's more close to original  'assign' tag. Changed 'customActionsFromTagExtensions' method for this.
* All examples are updated

ToDo:
* We have to mantioned special namespace + implemented custom tag  in notes to new DG version.