Typo in "Annotation" docstring.

The "axes fraction" description in the table of values for 'xycoords'
and 'textcoords' had a typo, suggesting that (0,1) represents the lower
left corner of the figure when it is actually (0,0).

I also removed what looked like an extraneous typo in the description of
the "figure fraction" property.

The corresponding table in the users guide was similarly updated.
Merge pull request #1748 from pbugnion/annotate_docs

Typo in "Annotation" docstring.