This is a great way to learn GIT. It also shows how you can embed a terminal in the browser for education purposes - try.github.io 
The console is based on CodeMirror - wikipedia
See also a comparison of Javascript editors - wikipedia
Atom is a free and open-source] text and source code editor for OS X, Linux, and Windows with support for plug-ins written in Node.js, and embedded Git Control, developed by GitHub - wikipedia
Most of the extending packages have free software licenses and are community-built and maintained. Atom is based on Chromium and written in CoffeeScript. It can also be used as an IDE.
For resolving Merge conflicts in git try using the Atom package merge-conflicts - atom.io
Note: install git-history
in git-history settings, uncheck "Show Diff"
show the git-history for a file
run spit-diff on your new and old file.
# See also * Add a project To GitHub * git-subrepo * git-subtree