Auto-generate documentation for chplcheck lint rules

[jabraham17]

Adds documentation for chplcheck rules, auto-generated from the existing chplcheck rule defintions.

This PR makes the following changes:

1. make docs will now build a rules.rst file which is included in the chplcheck documentation which lists all lint rules
   • This is enabled by the doc/util/chplcheck-docs.py, which is also available to users for their own custom rule files
   • Rules can also have examples, specified in tools/chplcheck/examples. These are included in the online docs and provide reasoning to users about why a lint rule exists
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2. The chplcheck langauge server will provides a link straight to rule documentation
   

Future work:

• Add more examples to tools/chplcheck/examples