Use flake8 for style tests
Ignore E261

For some reason flake8 wants two spaces before inline comments, let's
ignore that.
Ignore E128

This complains about indenting continuation lines - such as the items of
a long list - by four spaces, which is the style I prefer, so I'm
ignoring that error.
Remove superfluous line between methods
Remove superfluous space after ,
Add blank lines above function definitions
Add blank lines above module-level definitions
Fix worst cases of line length violations
Push max line length to 100

This allows going beyond the limit of 79 characters where that's
appropriate.
Perform style check on travis