Implement name_history.

This patch implements name_history in addition to name_show in libcoin.  I'm not sure if we should merge the patch here - instead, I'll also submit the patches to Michael Gronager, and he probably will merge them in libcoin/libcoin.  I think we should keep this repository to track libcoin/libcoin unless there are some changes that aren't going to be committed to libcoin/libcoin ever for some reason.  It seems that I can't submit a pull request against libcoin/libcoin directly - there must be something wrong with how the repositories are forked off each other.

I submit the pull request here nevertheless for reference.