Added TOTP implementation and tests.
Added documentation for TOTP.
Small fixes
Fixed documentation based on alexs' comments.
Updated secret key description
Added method definitions to TOTP documentation.
Updated HOTP and TOTP doctests
Added __future__ import statement
Fixed documentation
Fixed whitespace issue pointed out by flake8
Fixed wrong param naming in totp documentation
Seperated the totp tests based on different hash types
Merge pull request #637 from Ayrx/totp-impl

TOTP Implementation