Merged password hash and salt columns into one.
Explicitly support utf8 encoded passwords.
Added bcrypt password checking and automatic migration.

If the stored password hash is a bcrypt hash, the bcrypt checking routines are called. If it's an old-style password and matches, it is immediately upgraded to a new bcrypt-style hash.

The work-factor is fairly conservative, since the target platform for this application is a low-grade server.
Merge pull request #3 from edelooff/add-bcrypt

Add bcrypt