in knotkit/
 - twisted theory over U
 - add homology orientations for odd Khovanov homology and spectral
   sequence over Z
 - unify smoothing, resolution_diagram wiring (and knot_diagram?)
 - speed up construction of chain maps in chain_complex_simplifer
 - move chain_complex_simplifier to algebra/
 - unify chain_complex_simplifer and build_sseq
 - remove hardcoded limits (max_...)
 - revive testlib

in lib/
 - add hashset
 - between interoperation between sets that require bounds (bitset,
   ullmanset) and those that don't (set, hashset)
 - add make_pair, etc.

in algebra/
 - Q should use gmp
 - laurentpoly interface needs to be cleand up
 - add Zp
 - linear_combnation can be more efficient (eg no searching when
   coefficients die)
 - monomial ideals and maybe groebner bases
 - cleaner interface for gcd, etc. in fraction_field
 - support kernel, cokernel of torsion modules