For feature request #23
In addtion, I've removed the username/password/ip_address arguments for
the "login" action and replaced this with a "login_hash" argument, which
has to contain an encrypted (with a salt) string.
I enabled the "login_hash" argument for the "authenticate" action as
well, so it's possible to authenticate users without sending the
password in plain-text.

Using the actions without a hash would error out as the function didn't
have an user object to look at. It's now treating the user as a public
visitor and using those permissions.

Thanks @Xon!

Use parser factory method, rather than new.

The user hash used to be seperated by a column (:) like so:
USERNAME:HASH. This was later changed to use base64 encoding of the hash
instead. During this code change, the username prefix (USERNAME:) was
forgotten about and the API would therefore malfunction.

Addition to that, getUser() now fallbacks to the default XenForo visitor
if the API key isn't used.

This fixes #46 and #47

Use the static function instead of creating a new object