Clean up gemspec and ignore Gemfile.lock

Tools like Hoe and Jeweler were created back in the days where creating
gems and managing gemspecs were more difficult and a relatively new
thing to do. However, gem management has come a long way now! This patch
cleans up your Gemspec and removes hoe as a dependency. Additionally, it
adds a few nice little version constants so that people using the
library can easily access the version from their code if they want to!

Signed-off-by: David Celis <me@davidcel.is>
Oops that was an artifact from me thinking `extend Benchmark::BigO` was actually that `extend self` pattern