The full TOTP specification supports not only SHA1, but also SHA256 and SHA512. Up til now, the TOTP provider in this plugin (and most other PHP implementations) claims to support a specified hash type, but doesn't actually work with anything other than SHA1.

This is due to key lengths and hash lengths being _different_ for the three hash variants.

This change introcudes support for both SHA256 and SHA512, porting the implementation directly from https://github.com/ericmann/totp.

See https://tools.ietf.org/html/rfc6238#section-1.2 for more information on the `MAY USE` notation for SHA256 and SHA512.

See https://tools.ietf.org/html/rfc6238#appendix-A for a fully compliant reference implementation in Java.

See https://tools.ietf.org/html/rfc6238#appendix-B for test vectors showing TOTPs generated for specific time values and the three hash variants.

See https://github.com/ericmann/totp/blob/master/test/phpunit/ReferenceTest.php for example unit tests verifying this particular implementation before it was ported to the plugin.

This reverts commit 71c2cf5.