doc: Rewrite and overhaul of 'Compiler' page

[architeuthidae]

ARTIQ Pull Request

Description of Changes

Rewrite and overhaul of 'Compiler' manual page. Details on types and decorators. Attempts to clarify longstanding confusion points re: lists, arrays, etc.

Related Issues

Closes #1462 Closes #1162 Closes #717 Closes #656 Closes #1298 -- at least in that the behavior is now documented, and (pending NAC3?) still intended.

Does not close #1967, but it is related.

Type of Changes

	Type
✓	:scroll: Docs

Steps (Choose relevant, delete irrelevant before submitting)

All Pull Requests

• [x] Use correct spelling and grammar.
• [ ] Close/update issues.

Documentation Changes

• [x] Check, test, and update the documentation in doc/. Build documentation (cd doc/manual/; make html) to ensure no errors.

Git Logistics

• [x] Split your contribution into logically separate changes (git rebase --interactive). Merge/squash/fixup commits that just fix or amend previous commits. Remove unintended changes & cleanup. See tutorial.
• [x] Write short & meaningful commit messages. Review each commit for messages (git show). Format:

  topic: description. < 50 characters total.
  
  Longer description. < 70 characters per line
  

Licensing

See copyright & licensing for more info. ARTIQ files that do not contain a license header are copyrighted by M-Labs Limited and are licensed under LGPLv3+.