Add pep8 config, use pep8 in travis

also, fix E111-E113 errors:
E111 - indentation is not a multiple of four
E112 - expected an indented block
E113 - unexpected indentation

According to what you said earlier, this rule isn't enforced by the checkers you've enabled here (and anyway, to apply this rule, you often get indentations that are *not* multiples of four).