Moved production files and bag files into separate directory.
Development.

- bags are loaded from directory that is supplied via context or from the
  current directory.
- Generate() api added to programmatically generate output from supplied
  production grammar.
- added benchmark code for basic and simple productions.
Removed Attic directory.
golint on the source code.
Cleaned up `fmt` use cases.
Code refactoring.

- Print AST for production tree.
- Better error handling.
- Documentation.
Applied golint
applied errorcheck.
Fixes to benchmarking code.