Make label references "self-identify".

Prettyref provides a command \newrefformat, which specifies the way in which a reference is typeset, according to a label “identification”. The identification is set in the \label command, by using prefixed label names; so instead of \label{mysection}, one uses \label{sec:mysection}, and prettyref interprets the “sec:” part. The package is compatible with hyperref and with other packages.