While wmem is still nowhere near complete (it doesn't have an mmap block allocator, it doesn't have a red-black tree implementation), as of revision 45989 it should be able to replace emem in many cases.
I've put some documentation in doc/README.wmem which should explain its design and usage in sufficient detail.
At this point I'm happy enough with it to recommend it for more general usage (consider it a public beta or something along those lines). For the time being emem is still listed in README.developer, but if no major flaws show up in the next few weeks then I'm ready to switch that over and officially deprecate emem.
Please let me know if any of the documentation is unclear.
Thanks,
Evan