Case insensitivity

[Clemens Niederberger]

Add an option (at least) that makes chemnum's labels case-insensitive, i.e., labels \cmpd{test} and \cmpd{Test} would refer to the same compound. This would solve the problem reported on latex-community.org with \MakeUppercase, e.g., in headers.

[Clemens Niederberger]

chemnum is not developed further, its successor is xchemnum: https://github.com/cgnieder/xchemnum