Remember the original text of a Side.
Detect changes within each Side.
Change dirty detection to a property.

Since it's going to be called in an `editor:display-updated` handler, I don't
want to be doing a bunch of text comparisons if I can avoid it.`
Add a .dirty class to the SideView.
Apply a .dirty class to lines in a dirty hunk.
Style .dirty lines and SideViews.

Hide the revert button while until the side is dirty.
Fix button placement issues.
Mark it off in the README. :white_check_mark:
Merge pull request #4 from smashwilson/edit-in-place

Edit in place