Add TrueKeyword and FalseKeyword node types

[gregjacobs]

And TypeGuards for them too! ;)

[gregjacobs]

Btw man, just wanted to tell you, I'm making huge progress on this AngularJS->Angular2 converter thanks to you.

[dsherret]

@gregjacobs awesome! :) I can imagine that's quite complicated to do. I'd be interested to see it when it's ready.

[gregjacobs]

Man, I'd love to show it to you, but unfortunately I made the mistake of starting it in my company's system and that's where it is :(

I'm going to try to see if I can get approval to open source it though!

[dsherret]

BooleanLiteral will be available in the next version (whenever that's released).