Extend totalSizeInWords() to also return a count of capabilities, which helps when a separate capability table needs to be allocated as well.  Use this in the RPC system.

Make all Promise methods consistently consume the promise (returning a new promise when it makes sense), rename daemonize -> detach, and make eagerlyEvaluate() require an error handler (this caught several places where I forgot to use one).

kj::runIoEventLoop() is a shortcut for setting up an EventLoop that can do I/O, without specifying a platform-specific EventLoop.

Improve inf/nan.  This also makes GCC encode them consistently with Clang and with the existing testdata.

Improve test scripts, and add a new mega-test script which runs super-test on all platforms in parallel with progress bars.