We used to rely on out-of-tree git clones to be prepared by the user.
This commit changes the system to make sure we clone all git repos
we depend upon into the 'deps' folder, and then setup the symlinks
to that folder. As a result, we should be able to support
self-contained builds using the makefiles in this repo.
Importing in the Titan context apparently seems to mean symlinking the
source files into the current project. I haven't found a concept of
linking against libraries yet.