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/ast/mod.rs

@@ -0,0 +1,5 @@
+pub mod expr;
+pub mod stmt;
+
+pub use expr::*;
+pub use stmt::*;