move more things to zvshlib

preparation for tests, need to move more things to module
Merge pull request #44 from pkit/refactor

move more things from zvsh script to zvshlib package
some functional tests added
tests/functional: remove unused `json` import
zvsh: reimplement is_binary_string for py3 compat
zvsh: python3 fixes
tests/functional: python3 fixes
Merge pull request #46 from larsbutler/functional-tests

Functional tests