TST: Add inherited method

[larsoner]

A number of mostly small tweaks:

1. Fixes a minor typo
2. Adds an inherited method in test_full.py that hopefully will show (or be easily modified to show) the bug in BUG: Defer to autodoc for signatures  #221 with $self
3. Cleans up warnings in pytest
4. Fixes a bare except
5. Cleans up warnings in tinybuild
6. Runs tinybuild with warnings-as-errors

Should make things hopefully more robust. Might take a few iterations to get right depending on which Sphinx versions we support (I'll let the CIs tell me).

[larsoner]

@jnothman @rgommers this one should be ready to go, and should help with #221

[jnothman]

Is the idea that in the other pr this test should fall due to $self appearing?

[larsoner]

Yes, ideally. In your link it shows up in the HTML like:

<em class="sig-param">$self</em>

so I think it should work.

[larsoner]

... and if when I rebased #221 and cherry-picked my two commits here, it didn't work :)

So I actually simplified the code further and now it does work. No $self here, but there is a $self after rebasing #221 on this:

        # ensure that no autodoc weirdness ($) occurs
>       assert '$self' not in html
E       assert '$self' not in '\n<!DOCTYPE...dy>\n</html>'
E         '$self' is contained here:
E           ig-param">$self</em>, <em class="sig-param">/</em>, <em class="sig-param">*args</em>, <em class="sig-param">**kwargs</em><span class="sig-paren">)</span><a class="headerlink" href="#numpydoc_test_module.MyClass.__init__" title="Permalink to this definition">¶</a></dt>

[larsoner]

Okay since things are green let's get this in to keep things moving. Happy to make additional changes or roll things back if others look and see problems...