Refactor To Match Rust Standards

[ischeinkman]

All the direct extern bindings should be moved to a libnx-rs-sys crate, and libnx-rs should only contain a Rusty API wrapping that crate.

[leo60228]

For formatting it properly, try:

cargo fix --edition
cargo fix --edition-idioms
cargo fmt

[leo60228]

I've had some trouble with cargo fix when cross-compiling, but cargo fmt should work fine.