Helper binary for viewing function selectors

[sezna]

This is a small tool I just wrote to help validate @digorithm's spec. It is a bin package attached to core_lang which will parse a function declaration and return its function selector. Be gentle to it and don't be too fancy, the namespace is instantiated to be empty, so custom types and stuff don't work. Instead of stashing it or whatever, I thought it might be handy in the future, so here it is.

Usage

(in core_lang)

$ cargo run --features=selector-debug --bin selector-debug "fn entry_one(a: u64)"
selector string:         entry_one(u64)
untruncated hash:        0x0c36cb9cb766ff60422db243c4fff06d342949da3c64a3c6ac564941f84b6f06
truncated/padded hash:   0x000000000c36cb9c