Disable use of unit analysis (via kj::Quantity) by default (since it has some overhead), but enable it specifically for dev builds.

Fix capnpc-capnp.c++, which appears to have rotted (issue 15).  Should probably write a test at some point...

Don't check uncaught_exception at throw time because catchExceptionsIfUnwinding() is the correct way to handle it.

Enable some useful Clang warnings, fix some bugs it detected.  Especially, eliminate all dynamic initializers.

Mark every destructor "noexcept(false)" unless it is very clearly noexcept.  The change in C++11 making destructors default-noexcept was a mistake.

Add mechanism for catching exceptions that has limited use even with -fno-exceptions, as well as a mechanism to detect when a destructor is called during unwind and to avoid throwing in these situations.

Use consistent naming style for structs that exist purely to specialize template aliases or functions.