Run compiletest on rmc documentation code

[tedinski]

Description of changes:

A few findings:

1. Compiletest does weird things and seem very insistent on the convention of putting everything under src/test/ so I created a symlink. (Github doesn't seem to indicate this very obviously, but that's that src/test/rmc-docs is.)
2. Its behavior seems to just be find . -name "*.rs" and compile each file separately, but that's fine for the doc tests, since we're only using the proptest dependency if cfg(test) which we aren't here.
3. All but one doc test is rmc-verify-fail but that's fine I think since we mostly want to ensure they still build correctly. It'd be nice if we could be more precise about why they fail, but that's not easy to do, so oh well

Resolved issues:

Resolves #254

Testing:

• How is this change tested? it's new tests

• Is this a refactor change?

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[adpaco-aws]

LGTM modulo the comment below.

[adpaco-aws]

I thought testing rmc-docs examples was going to be done by the build-docs.sh script (see the TODO comment there).

I'm okay with having it here but then we should remove the comment. Does the regression workflow need to change too? Please check.

[tedinski]

Ah good point! I'll remove the comment and add another bit of documentation about how to run the tests for the docs.

The CI workflow runs the rmc-regression.sh script.

[adpaco-aws]

Right, but I recall having a discussion with you about the condition to execute build-docs.sh. Anyway, looks like it executes on Ubuntu 20.04 only - that is fine if we run them from rmc-regression.sh.