Split install action into the new crate cargo-gpu-install

[Firestar99]

Requires #128

See primary issue #105

Superseding #112 and #117

• extract the "install" action to the new cargo-gpu-install crate
  • philosophy: keep it as simple as possible, while removing cli deps
  • About the name: I felt like it was more descriptive than my previous suggestions with *-cache
• has the following features to make these dependencies optional:

clap = ["dep:clap", "spirv-builder/clap"]
watch = ["spirv-builder/watch"]
tty = ["dep:crossterm"]

• removes a few dependencies too: env_logger, relative-path, serde_json, semver, dunce
• serde is not worth feature gating, since spirv-builder itself needs serde and serde_json
• best reviewed commit-by-commit

close #105

[Firestar99]

This line is already adjusted for Rust-GPU/rust-gpu#488, even though it is not yet in this branch. So this will fail doctests (which we don't test in ci...)

[tombh]

Looks good!

What about adding a section in the main README about the 2 ways (as a CLI and as a crate) of using this project?

I think that the only reason crossterm is used is to enable pressing y without hitting return to accept the confirmation? It's not a big deal, just worth bearing in mind. I think it's actually probably more conventional to not have to hit return with these kind of prompts.

[Firestar99]

Kept the readme update simple: https://github.com/Rust-GPU/cargo-gpu/blob/install-crate/README.md (and updated the cargo-gpu-install readme to not mention wgsl stuff)

On crossterm, yes that's the only thing we use it for. Which is why I just hid it behind the tty feature along with user output, which realistically noone should enable other than cargo-gpu itself. Also optimized the features of it to remove some extra deps.

[Firestar99]

Let's move the entire readme discussion to #133, since I think it needs a lot more than just mentioning the crate dependency path. (Also I hid your large comment)

Primarily, I made this over the past few weeks: https://github.com/Rust-GPU/rust-gpu-template
(and have given it a readme literally an hour ago)