Composer.lower

• The composition json is now just the AST with no implicit lowering.
• composer.lower(composition, [combinators]) is now exposed and gives control over the lowering (if desired).
• The compose command has two new options: --lower and --version.
• The combinators are now automatically derived from spec, e.g, if: { args: [{ _: 'test' }, { _: 'consequent' }, { _: 'alternate', optional: true }], since: '0.4.0' }.
• The spec for the combinators is now exposed as well (composer.combinators).
• The core language has shrunk thanks to composer.mask and a more aggressive use of lowering.
• The fsm has fewer states.
• The code is now split into three components: 1 compiler component available client-side and server-side, 2 client-side composer, and 3 server-side conductor.