Speed up dependency matching

When searching for a specific name, we can just do a binary search to find the gems by their name, instead of iterating thru all the gems (which takes a long time, since there are over 320,000 gem versions).
To do this, we need to sort the tuples by name, which is just a little overhead.

Motivation:
Gem update took 32 seconds on my machine, when there was nothing to update, only to check if there is a newer version.
With the optimized version, it dropped down to 2 seconds.
Merge pull request #595 from sullerandras/speed_up_dependency_matching

Speed up dependency matching through #bsearch