[m12] code2fn documentation and unit test updates (#860)

## Summary of Changes
### Documentation Updates
Updates the endpoint documentation for the following Code2fn services
- code2fn
- execution_engine
- comment_extractor
- workflows

Additionally, adds a new page to the Github site documenting how to add
support for dependency generation for new languages.

### Unit Tests
Adds unit tests for Fortran->CAST to reach parity with Python unit
tests.

### Bug fixes
Fixes bug where extra Name node could be generated at the end of
function definitions
Fixes bug in Loop generation where the wrong loop type could be ingested

### Related issues
#849
#858
#839

Resolves #858
Resolves #839 275bd97