v0.7.0

Added

• Added a project context to Myriad context that comprises all of the data
  available at pre compile time that is useful to code generation, especially
  when generating a typed Ast.
• Added more extensions to Ast nodes so they can be constructed easier.

Changed

• Altered the generation code to use plain Ast nodes rather then wrapper records, in
  the long term depreciating Rcd prefixed types from FsAst, simple extensions are preferred
  and less verbose.

Breaking

• Altered the plugin API so that both Ast and string based output are possible via a
  discriminated union return type.