[feature] Support standalone installation and other runtimes

[DreamOfIce]

Thanks for proposing a new feature!

Motivation

Standalone

For many users, they may wish to use another wasm runtime for some reason, when bundling with wasmer can take up a lot of unnecessary disk space.

Other runtimes

I hope wapm can support other runtimes like wamr, wasmtime, etc.

Proposed solution

• It looks like the release is a standalone version, can you write an install script and guide for this?
• About other runtime support, maybe add an option to customize the runtime location?