This commit adds truncated 2-quotients, groupoid quotients, Eilenberg MacLane spaces, chain complexes, the long exact sequence of homotopy groups, the Freudenthal Suspension Theorem, Whitehead's principle, and the computation of homotopy groups of almost all spheres which are known in HoTT.
This renaming is because type_quotient is a nonstandard name. I've had a discussion with Egbert
Rijke, Steve Awodey and Dan Licata, and the consensus for a better name was 'quotient'. I had to
make changes in src/kernel/hits/hits.cpp, I renamed g_type_quotient* by g_hit_quotient* (to avoid
name clash the standard library quotient, although I don't know whether that name clash would
matter).
