WIP: Re-implement parser in pest

Parser implementation is kind of iffy. Let's try to re-implement it
using pest.

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

src/syn/mod.rs

@@ -2,5 +2,6 @@ pub mod ast;
 pub mod error;
 pub mod lexer;
 pub mod parser;
+pub mod peg;
 pub mod span;
 pub mod token;