Updates to get the authentication backend working

devel.cfg had default parameters 'pass' and 'db', while the parameters needed in src/Snap/Snaplet/MysqlSimple.hs (from line 198) are 'password' and 'dbname'.

CreateTableIfMissing in src/Snap/Snaplet/Auth/Backends/MysqlSimple.hs used postgres syntax. Changed this to the much simpler MySQL syntax.
Varchar columns require a length in mysql.

After making these changes on my local copy of the snaplet, Snap could create the snap_auth_user table with the correct columns. RegisterUser now correclty writes new users to the snap_auth_user table in MySQL.