WIP: Implement peg parser using pest

PEG parser using pest is implemented. It was able to run the three
examples that we currently have so hopefully there aren't any huge
issues. There's a few warnings remaining that I will squash soon. Token,
parser, and token modules have been removed.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/syn/mod.rs

@@ -1,7 +1,3 @@
 pub mod ast;
-pub mod error;
-pub mod lexer;
-pub mod parser;
 pub mod peg;
 pub mod span;
-pub mod token;