Rust Port available

[jwurzer]

Hi!
Now I have ported Bantam also to Rust.
It is available at https://github.com/jwurzer/bantam-rust.
It would be great if you put a reference to the Rust port in your Readme file so that my Rust port can be found easily :-)

This Rust version is similar in structure and design to the original Java version. The error handling is done with the panic! macro for simple unrecoverable error handling in the master branch. For error handling with recoverable errors the branch with-error-handling exist. This with-error-handling version is a little bit more complex but has the advantage that the program does not terminate immediately in case of a wrong parsed expressions.