some of the changes are backported from the hott3 library
pi_pathover and pi_pathover' are interchanged (same for variants and for sigma)
various definitions received explicit arguments: pinverse and eq_equiv_homotopy and ***.sigma_char
eq_of_fn_eq_fn is renamed to inj
in definitions about higher loop spaces and homotopy groups, the natural number arguments are now consistently before the type arguments
All HITs which automatically have a point are pointed without a 'p' in front. HITs which do not automatically have a point do still have a p (e.g. pushout/ppushout).
There were a lot of annoyances with spheres being indexed by N_{-1} with almost no extra generality. We now index the spheres by nat, making sphere 0 = pbool.
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.
