Add therubyracer or bundler breaks $LOAD_PATH

Bundler prunes Ruby's $LOAD_PATH down to only gems that are listed in
`Gemfile` and their dependencies. When a package does not explicitly depend on
a particular gem, as *execjs* does because it is able to use any of
several JavaScript engines, it gets removed from the load path. I have
been unable to find a way to configure bundler to not do this. The other
alternative would be to remove the Gemfile altogether (or maybe rename
it to something not default).
Rename "pygments" to "highlighter" for Jekyll 2
Remove Gemfile.lock; not applicable here really
Ignore Gemfile.lock too