Allow using secret of type "bytes"

[beebeeep]

So far library assumes that secrets are strings which leads to certain complications in python3, namely it is impossible to use random binary vectors as secret as python3 string should be valid in terms of specified text encoding. Also constructions like 'keys' in key may lead to some unexpected behaviour if secret contains substring "keys". This changes makes key parsing logic a bit clearer and allows to use bytes strings secrets.

Also I believe that would resolve #74 and #72

[codecov-io]

Codecov Report

Merging #93 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #93   +/-   ##
=======================================
  Coverage   93.58%   93.58%           
=======================================
  Files          13       13           
  Lines         998      998           
=======================================
  Hits          934      934           
  Misses         64       64

Impacted Files	Coverage Δ
jose/jws.py	94.11% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 55b6556...0b63471. Read the comment docs.

[beebeeep]

Anyone?

[blag]

I'd be interested in merging this if you can add tests.

[blag]

Thanks!