p.s. thanks @cstrahan for vim syntax highlighting

Eliminate the concept of imbuing messages in favor of the simpler concept of setting a cap table directly on MessageReader / getting one from MessageBuilder.  This eliminates capability-context entirely.  This was made possible by the earlier change which moved capabilities to a separate table rather than storing CapDescriptors inline, but I didn't realize it at the time.

Split libcapnp into three libraries:  libkj, libcapnp, and libcapnpc.  The third contains the schema parser.  Unfortunately it is rather enormous so we should give people the option to not link it.

Apply some capnproto -> capnp renames that didn't happen before, update docs, put samples in a place where they are easy to compile.