[Feature request] Ability to specify starting time (T0) for TOTP

[krt222]

Hey!

It would be nice if users of this package could specify the starting time (T0) for TOTP (T0). Currently all users are forced to use T0=0 (Unix epoch).

Thank you!

PS: There is a small typo in the help page of TOTP which I do not know if it justifies opening a new issue. HOTP$verify(code, t, behind = 0L) should be TOTP$verify(code, t, behind = 0L)