add sha256 and sha512 support for totp

[jonas-w]

This fixes #171.

• The code now extracts the algorithm, digits and period query parameter from the totp URL too.
• parse_totp_secret now returns the TotpParams struct
• generate_totp now uses the totp_params.algorithm to pass the correct hash type to totp_lite::totp_custom.
  • Code duplication seems to be "necessary" as the hash type needs to be known at compile time, or at least I couldn't figure out another way.
• generate_totp also uses the parsed number of digits and the time period.
• There should be no behaviour changes compared to the previous version of the code for URLs without these parameters.