Added HOTP implementation and associated tests
Added documentation for HOTP implementation.
Minor changes for python3 compat and documentation changes
Updated according to code review feedback.
Updated documentation.
Added a max limit of 8 on length parameter. Updated documentation.
Updated docs with notes on throttling and resynchronization.
Final changes to module names
Updated documentation.
Changed module name from otp to twofactor.
Added "version added" to docs
Fixed HOTP test path, added changelog and myself to author list.
Merge pull request #598 from Ayrx/hotp-impl

HOTP Implementation