stop overflowing RTD subprocess buffers

[svenevs]

It seems that medium to large projects cause problems on RTD.

• [x] Stop colorizing output on RTD, they don't let you have color (:rage:)
• [x] Suppress doxygen output with /dev/null on RTD

The hacky silent branch verified that exhale is the cause of cat conf.py being the last step before failure.

If anybody ever reads this, one way to test exhale is generate the full api and track it on git (you can force-push this away, or do it on a different branch altogether and kill that branch).

Suppose you got

• docs/
  • api/
    • library_root.rst and all the others
  • doxyoutput/
  • conf.py

Then you want to locally make html once. Now git add -Af api/ doxyoutput so that all the generated reStructuredText and doxygen files are going to be available in a clone. Now edit conf.py and comment out the exhale entry in extensions and anything else exhale related (don't forget to git add conf.py changes).

Hopefully you shouldn't need to do this, but it can help identify where the problem is. In this case, doing that produced a successful build, so clearly exhale is the problem!