Rubygem conventions

These commits make the clever-ruby gem a bit more idiomatic, in my opinion. I understand if you choose not to merge any or all of this, though :)

There was some commented-out code for an rcov rake task-- that's a pet peeve of mine, if we ever need that code again, git will save it for us in the history :)

Bundler actually provides simple rake tasks and conventions for building gems, and many gem authors are going with that these days. So I removed the dependency on Jeweler and just used bundler to set up and manage the gemspec, building the gem, etc.

Naming conventions of gems, their directories, and their namespaces are not rigidly enforced across ruby gems, but I think naming the directories the same thing as the gem brings this into line with more existing gems (and I have a few examples in the commit message).

If you like these changes, I'd recommend pushing v0.0.1 out to rubygems.org if only to claim the clever-ruby name.