Initialize Aster project with basic structure, including Cargo configuration, lexer, parser, interpreter, and AST definitions. Add a sample script and README documentation. Implement basic error handling and environment management for variable storage.

src/lexer/mod.rs

@@ -0,0 +1,5 @@
+pub mod token;
+pub mod lexer;
+
+pub use token::{Token, TokenKind};
+pub use lexer::Lexer;