GoogleDocstring does not handle new xref format well

[dandhlee]

Previously, when xrefs were included for GoogleDocstring it crashed, not knowing how to process it. To work around this, I've took xrefs out of the equation, ran GoogleDocstring, then added them back in. Tedious, but worked. Also included test cases.

However, with the new format of xrefs with <xref uid="uid">text</xref>, this was not considered as the previous grep for "xref:" were the only ones included in the unit test, and not with the new format, thus it hasn't worked out well.

Interestingly enough, I'm not sure why it took ~60 repos to find that this would fail, rather than it failing before...