border bug, and `σjofk` bug (#32)

* border is computed from the point which is always in
* bug fix σiofk, σjofk
* version bump
* update CI

use only wignerd_doublearg_sign in amplitude

proper border function

Merge pull request #3 from mmikhasenko/refactor

Update of API: more strictures, Invariants

factored out the PartialWaveFunctions

The first tagged version