Ubuntu 14.04 dependency libgit2-0

[neuralsandwich]

It may be good to add libgit2-0 as a dependecy for Ubuntu users to install. That fixed my only installation issue :D

[kbenzie]

Yeah I'm planning adding the option to use the system version of libgit2 for building and runtime as well as being able to build and install it as part of the project. When I tested it using the CMake install target libgit2 was installed as well as git-prompt so I didn't see this problem.