move 'options' to 'run_diff' method

added 'cmd' argument support, so you can assign an external editor us…

…ing kwargs instead of settings

updated README and fixed whitespace

fix attempt for 'ValueError: path too long for Windows'

FIX

readme update and misc fixes. resolves colinta#26 and colinta#31.

Merge branch 'st3'

fix newline bug

Merge pull request colinta#20 from BelokrysFedotov/patch-1

Update README.md

refactor of run_diff to support internal (in sublime), external, or b…

…oth, and using @jiriurban's tempfile support.