Convert from hoe to bundler

Switch gem management from hoe to bundler, for new contributors being able to
do `bundle install` is easier and more familar than hoe, and  bundler is
simpler to than hoe for dependency management.

I had to replicate the functionality some of the plugins provided myself
but it has the same spirit as before. If there's any tasks I've missed that
you'd use regularly let me know and I'll try to help.

If you'd prefer to stick to hoe, would you consider an alternate PR adding
in a gemspec for the master branch? As without a gemspec bundler seems to
refuse to consider this as a git dependency.