add regression test for complex number

Copy of Handle spaces before comments

Fix markdown syntax for link to code of conduct

This allows comments that are preceded by a space to be detected
and processed with the comment

Remove dead code from render.py module

Convert readthedocs links for their .org -> .io migration for hosted projects

As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:

> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.

Test Plan: Manually visited all the links I’ve modified.

[fix] remediate race when creating cache file

If another process writes the cache file while we were generating the grammar, we'll fail to run os.open(cache_file, os.O_RDWR | os.O_CREAT | os.O_EXCL, 0o0600) because the file (now) exists.

Common errors

A test testing bad indentation using python3 led to a bad fix by adding
an UnexpectedIndentation exception. In fact, the root cause was
a discrepency between python2 and python3 for comparing None values to
string. The added exception and try catch was thus hiding this.

This commit fixes the problem correctly by handling None values
similarly in python2 and python3. It highlights also where does the None
value comes from.

It was not testing if the UntreatedError was a BaronError child.