Python specific `fill-column' enabled, lp:1037454

Customize new boolean `py-set-fill-column-p'. If `t', reads
`py-docstring-fill-column', default is 72
and `py-comment-fill-column, default is 79

Comment- and docstring settings might be disabled by
any non-integer value, which means: do not use a
different value of `fill-column' than emacs-wide
py-up fixed

Minor API change:
- If inside a delimited form --string or list-- go to it's beginning
- If not at beginning of a statement or block, go to it's beginning
- If at beginning of a statement or block, go to beginning one level above of compound statement or definition at point.
py-down fixed

Minor API change:
- Go to beginning of one level below of compound statement or definition at point.
- If no statement or block below, but a delimited form --string or list-- go to it's beginning. 
- Repeated call from there will behave like down-list.