Fix obscure bug where the last outgoing message (and any capabilities therein) would not get released (until a new message was sent, replacing it as the last).

This took hours to track down, because it initially looked like "Release" messages weren't being honored in some cases (when they happened to be releasing a capability from the last message, and no subsequent messages were sent). Initial attempts to capture this in a unit test failed because the test of course used a subsequent call to detect if the capability had been released, which succeeded.

For portions currently copyright by Kenton (most of it), transfer copyright to Sandstorm Development Group, Inc. (Kenton's company).

The license change is practically meaningless, as MIT and BSD 2-clause are legally equivalent. However, the BSD 2-clause license is sometimes confused for its ugly siblings, BSD 3-clause and BSD 4-clause. The MIT license is more immediately recognizeable for what it is.

Rémy Blank and Jason Choy (the two non-trivial contributors) are on record as approving this change:

https://groups.google.com/d/msg/capnproto/xXDd2HUOCcc/gbe_COIuXKYJ

Get rid of 'Advanced' server methods, just have one method that takes a CallContext.  A typedef reduces boilerplate.

Implement opt-in cancellation for local calls.  (Previously, cancellation would happen whether or not the callee had opted in.)

Tail calls half-implemented, but I think it's time to delete all the cancellation code before continuing because it will simplify things.

Implement two-party network.  The first RPC call over a socket took place at 2013-11-08 14:46:43 -0800 and completed successfully.

Delete Code Friday:  Inline structs/lists/data are too complicated for not enough benefit.  There goes a week of my life that I'll never get back.