Put everything into namespace Boom::
Add task `rake a`
fix: Add namespace
Add Unit

Allow `def f()` (Unit -> X)
and `def f(x: Int) end` (X -> Unit)
Use parslet instead of racc (wip)
Add some rules
Fix parser to pass parser_spec.rb
Fix parser to pass normalizer_spec
Fix to pass evaluator_spec
Merge branch 'peg'