* Migrate to `unittest2`
why:
Global symbol overflow when running NIM 1.2 on Github ci suggests that
unit tests run sort of separately. The replacement library `unittest2`
provides that.
* Build ci dependencies
* The bit procs defined over number values and openarray are now part of
the bitops2 module and use the more traditional LittleEndian indexing.
* Added BitSeq and BitArray types as defined in the ETH2 spec.
Jordan Hrycaj
Jacek Sieka
Zahary Karadjov