Put column descriptions where they belong

The Column class accepts a 'doc' argument. Use it.

And while we're at it, make them all unicode strings.

Performed by the following sed script:

   s/info=dict(description=u\?\("[^"]*"\))/doc=u\1/
   s/info=dict(description=u\?\('[^']*'\))/doc=u\1/
   s/\(\s*\)info=dict(description=u\?\("[^"]*"\), /\1doc=u\2,\n\1info=dict(/
   s/\(\s*\)info=dict(description=u\?\('[^']*'\), /\1doc=u\2,\n\1info=dict(/

   /info=dict(description=u\?\('[^']*'\),$/ {
       s//doc=u\1,/
       n
       s/^\s*/&info=dict(/
   }
PEP 257, yo

Put the closing quote of single-line docstrings on the same line, and
end with a period.

Just tables.py for now.
Address some XXX comments
Remove some lies about encounter slots