Move pretty-printing to its own module.

src/syntax.rs

@@ -2,6 +2,7 @@ use codespan_reporting::{diagnostic::Diagnostic, files::SimpleFiles};
 use lalrpop_util::lalrpop_mod;
 use logos::Logos;
 
+pub mod ast;
 mod location;
 mod simplify;
 mod tokens;
@@ -10,7 +11,7 @@ lalrpop_mod!(
     parser,
     "/syntax/parser.rs"
 );
-pub mod ast;
+mod pretty;
 mod validate;
 
 pub use crate::syntax::ast::*;