In RPC protocol, rename request -> params, answer -> results.  Also fix up Join stuff in rpc-twoparty.capnp, because it was sort of wrong.
Simplify event queuing -- always preempt from same thread, yield cross-thread.
Fixes #39 - race conditions in promise framework.
Split WorkQueue into a separate file.
Fix races in WorkQueue, and simplify usage.
Lockless EventLoop, but at what cost?  This code got weird.