[RFC] more agressive error check for `make docs`?

[Andrew Bennetts]

Alexander Belchenko wrote:
> Currently `make docs` always runs successful even if there is
> some warnings or errors during html generation. I think it's bad,
> because periodically I find regressions.
> 
> Can we adding some flags for rst2html.py to have non-zero exit code
> for such situation? Because docs generated during `make check`
> and IIUC it's used in PQM, we have another blocker for regressions?

I think this is a good idea.

-Andrew.