added 2-1 division using Newton inversion with a precomputed inverse
added modular multiplication with a precomputed inverse
added modular powering with a precomputed inverse
added modular Brent-Kung composition with a precomputed inverse
changed distinct degree factorization so as to use precomputed inverse versions, less gcd's,
and less modular compositions
added benchmark test
added docu of mulmod_preinv
added docu for 2-1 division with precomputed inverse
added docu for powmod_ui_binexp_preinv
added docu of compose_mod_brent_kung_preinv
added profile test for modular multiplication with precomputed inverse
fixed a bug in distinct degree factorization
fixed a memory leak
promote Martin Lee to 'significant contributor'
change cutoffs for nmod_poly_factor: KS now usually wins, except for small degrees where CZ is still fastest