Change formatting: 90 cols, IndentPolicyFree, etc. Add brittany.yaml

Most people have pretty wide and high res screens at this point. I
can't fit two windows with 100 line length next to eachother with my
font size, but 90 works and most people have smaller font size than me
I think.

Also, change brittanys indentation policy to Free. This almost always
looks better. I just had to disable formatting of imports -- I don't
want to align those, but IndentationPolicyFree insists.

Finally, actually add a project-local brittany config file, so that
anyone (or me in the future / on another computer) can use the same
formatting rules.