feat: Add a README.md and logo.svg.

This commit adds the `Token` and `TokenKind` definitions in `src/token.rs`,
in `src/lexer.rs` I've added the `Lexer` logic.

examples/hello-world.bky

@@ -1,5 +1,3 @@
-extern puts(text: *char);
-
 fn main() {
     puts("Hello, World!");
 }