- Lexer/Compile exceptions propigate throughout lexer/parsetree/ast

using a more portable **exception_kwargs collection
- added "source" member to the dict propigated to Lexer/Compile exceptions
- RichTraceback can access original template source as a unicode object
using either 'source' memebr on Lexer/Compile exception, or 'source'
property on ModuleInfo, fixes #37
- unit tests for #37