Add HOTP support to core and all major backends

Remaining support for provisioning, both in cgi and totpprov
Switch to HOTP counters starting from 0

Using counters starting with 1 breaks yubikey's HOTP support, as it
either has to start from 0, or be a multiple of 16.
Fix HOTP tests to expect 0-based HOTP counter
Add --hotp support to totpprov

Also print out the ykpersonalize commands one would need to run
to burn the yubikey.
Add vref part of the gitolite support
Add command part of the gitolite support
Add README and clean up commands

Ready for a master merge and a 0.6 pre.
Document --hotp flag in the totpprov command
Up version to 0.6.0-pre