2695: Pretty print of -x/y

Implemented one possible solution: Shift denominator one character
to the right when certain conditions apply:
- Numerator is negative,
- Numerator is even width,
- Numerator is wider than denominator.
2695: Pretty print of -x/y

Implemented one possible solution: Shift denominator one character
to the right when certain conditions apply:
- Numerator is negative,
- Numerator is even width,
- Numerator is wider than denominator.
Merge branch '2695_pretty_print_fractions' of github.com:nelsoner193/sympy into 2695_pretty_print_fractions

Getting everything to play nicely together, while making sure my branch
is updated.
2695: Pretty print of negative fractions

Added tests, normalized some things, and improved the method for
printing negative fractions: If the numerator is negative, we
simply pad the numerator's width with a space on the right to
match the negative sign spacing.
2695: Pretty print of negative fractions

Removed commented-out debugging lines. Whoops.
Merge branch 'master' into 2695_pretty_print_fractions
2695: Pretty print of negative fractions

Fixed up doctests, fixed some code quality errors introduced by
said fixing of doctests and other mistakes.
Merge branch 'master' into 2695_pretty_print_fractions
Merge pull request #2172 from nelsoner193/2695_pretty_print_fractions

2695: Pretty print of -x/y