Make a few tests pass by doing something weird

Suddenly I need to refer to the parser's root rule rather than the
parser object iself?

>> Smashcut::FountainParser.new.parse "INT. APARTMENT - NIGHT"
TypeError: no implicit conversion of Parslet::Atoms::Entity into Integer
        from /Users/maxjacobson/.rvm/gems/ruby-2.0.0-p353/gems/parslet-1.6.0/lib/parslet/atoms/context.rb:88:in `[]='
        from /Users/maxjacobson/.rvm/gems/ruby-2.0.0-p353/gems/parslet-1.6.0/lib/parslet/atoms/context.rb:88:in `set'
        from /Users/maxjacobson/.rvm/gems/ruby-2.0.0-p353/gems/parslet-1.6.0/lib/parslet/atoms/context.rb:34:in `try_with_cache'
        from /Users/maxjacobson/.rvm/gems/ruby-2.0.0-p353/gems/parslet-1.6.0/lib/parslet/atoms/base.rb:83:in `apply'
        from /Users/maxjacobson/.rvm/gems/ruby-2.0.0-p353/gems/parslet-1.6.0/lib/parslet/atoms/base.rb:70:in `setup_and_apply'
        from /Users/maxjacobson/.rvm/gems/ruby-2.0.0-p353/gems/parslet-1.6.0/lib/parslet/atoms/base.rb:30:in `parse'
        from /Users/maxjacobson/Dropbox/src/smashcut/lib/smashcut/fountain_parser.rb:112:in `parse'
        from (irb):12
        from /Users/maxjacobson/.rvm/rubies/ruby-2.0.0-p353/bin/irb:12:in `<main>'
>> Smashcut::FountainParser.new.root.parse "INT. APARTMENT - NIGHT"
=> [{:scene_heading=>"INT. APARTMENT - NIGHT"@0}]