htmldiff: initial ugly integration of htmldiff.js library

This appears to be a better written library and I think a more promising
route moving forward.  There are some parts of the resultant output
that are not desirable right now, but I think some of that can be resolved
by some cleanup and styling changes.
Merge pull request #114 from sbenhaim/htmldiff

htmldiff: initial ugly integration of htmldiff.js library