compilers/source: Add changes allowing enum & const syntax
compilers/source: Add changes allowing enum & const syntax

Changes:
- `const` and `enum` nodes now store values in compiler state
- `parser:transform()` searches through constants and enumerations first
- `-- @<directive>` lines are now supported
  * `-- @module <module name>` now initializes and auto-returns _ENV

RyanSquared/FusionScript