Add runtime library and example assembly

Add runtime library and example assembly

This is further exploration into what the code could look time, but this
time there were productive results. This has a few parts:

- The runtime is written as Rust code! It's almost 100% unsafe code
  because I didn't want to think about safety boundaries with the
  assembly code that's outside the runtime. I can probably end up making
  almost all of it safe code with a little bit of work.

- The code mostly works by constructing lambdas with the runtime
  function, and then lambda bodies are mostly just applying objects to
  each other with the ivy_app function.

This sample program implements doing arithmetic on Church numerals, and
then uses it to run the debug print 64 times.