add LICENSE
add gemspec
add basic code generation logic

Bootstrap module controls conversion from raw AST to things that know how to
compile themselves (i.e. Code), via #expand.

Compilation strategy is similar to before; Code defines #bytecode which takes
a generator and a module. They generate code on the generator and use the
module for compiling sub-code (e.g. `mod.compile(gen, somenode)`.

Organization of these Code classes is TBD. Right now they're just under Atomy.