[Yhc] Warning, API change in Yhc.Core.FreeVar

Hi, I have developed the API using the word Free to mean both Free and Bound. This is not good. As a result I'm going to be changing most of the terminology in the library, and pretty much guarantee to break all the people using this API. I don't think thats many people, in fact it may well just be me, but before breaking API's I thought I'd let everyone know. The patches should be coming along in about half an hour. Thanks Neil