Add rust_calltree.pl

[satanson]

Add rust_calltree.pl to show calling and called relation of funtions in Rust project.

[hanxuanliang]

I recently looked at Rust Project(like sled), suddenly thought of this tool.
Not sure when the RUST version will be released 😂

[satanson]

@hanxuanliang type-oriented language is quite difficult to generating class hierarchy via regex extraction. I think it needs more powerful tools like static analysis tools.