contains OSX mixer

memcmp() can overflow the buffer.

Allows eliminating lots of complexity and workarounds for bogus
assertion failures.

We now pass the EventThread's EventLoop reference around.

This is only needed while Run() is alive, and moving it there avoids
problems with thread-checking assertions.

Our local EventLoop instance was never run; it was not usable.

Add API documentation
Support 64 bit offsets
Use InputStream for all reads

Fixes Mac build failure.