* A bultin patcher providing interfaces for custom types that can be represented as standard go types for expressions.
* Move node creation inside of loop.
* Reorder imports. Fix some formatting.
* Rename expr function from 'getExprValue' to '$patcher_value_getter'.
* Move to expr-lang
* Rename Patcher to ValueGetter
* Remove use of Expr in naming
* Rename interface functions to use 'AsType()' convention
* Document motivation and an example use case
* Add example usage to AsAny()
* Move under patcher directory
* Fix reference to old import path
