Fix nbsp breaking tables (#629)

[Crozzers]

This PR fixes #629, which was caused by a nbsp on the end of a table.

The true cause was the whitespace trimming regex in the tables extra:

python-markdown2/lib/markdown2.py

Line 3579 in 03d2391

trim_space_re = '^[ \t\n]+|[ \t\n]+$'

This regex matches spaces, tabs and newlines but misses all other forms of whitespace. Replacing these character classes with a simple \s fixed the issue

[nicholasserra]

Thank you!