MINOR: Add "sigalg" to "sigalg name" helper function

MINOR: Add "sigalg" to "sigalg name" helper function

This function can be used to convert a TLSv1.3 sigAlg entry (2bytes)
from the signature_agorithms client hello extension into a string.

In order to ease debugging, some TLSv1.2 combinations can also be
dumped. In TLSv1.2 those signature algorithms pairs were built out of a
one byte signature identifier combined to a one byte hash identifier.
In TLSv1.3 those identifiers are two bytes blocs that must be treated as
such.