Consider src/bin/goga.rs instead of src/main.rs

[dlight]

I know that having both src/lib.rs and src/main.rs is suggested in the second edition of the Rust book, but for a crate that already has src/lib.rs, it's more typical to have src/bin/goga.rs instead.

Some links:

• Rust package with both a library and a binary?

• Publishing a crate containing both lib.rs and main.rs files