Remove parse_next from TokenStream public interface

Same reason as in c776f7.

src/main.rs

@@ -308,7 +308,7 @@ impl<'a> TokenStream<'a> {
 		self.cursor += length;
 	}
 
-	pub fn parse_next(&mut self) -> Option<Token> {
+	fn parse_next(&mut self) -> Option<Token> {
 		let mut chars = self.chars();
 		
 		let token = match chars.next()? {