User control of ignored changes

[mgree]

Right now ignore_changes is using logic that's only appropriate for the hs stuff. We should (a) have nothing be ignored by default and (b) let the user specify what to ignore.

I imagine:

$ try -i '*~' -i '#*#' -- emacs -nw foo.txt
...

We should allow multiple instances of the -i flag, with the expectation that these will be passed as patterns to grep -v.

Somewhat related to #25.