feat: Add Expression definition and parsing logic.

src/main.rs

@@ -1,11 +1,11 @@
-use crate::token::Tokenizer;
+use crate::parser::Parser;
 
+pub mod ast;
+pub mod parser;
 pub mod token;
 
 fn main() {
-    let input = include_str!("../example/main.bky");
+    let mut parser = Parser::new("user.age >= 18");
 
-    for token in Tokenizer::new(input) {
-        println!("{token:?}");
-    }
+    println!("{:#?}", parser.parse_expression(0));
 }