The standalone compiler should support cross compilation

[CompeyDev]

As of now, it isn't very straightforward to use the standalone compilation feature to support various platforms with lune. Lune should build on top of this system and include a cross-compilation system similar to tools such as pkg for node. This issue suggests a strategy to implement the aforementioned.

Proposed Implementation

1. The build command should include two new flags: --base and --target, both to be used mutually exclusively. 

2. Lune should maintain a target database at ~/.lune/targets. These would be collections of precompiled binaries for different platforms that can be readily patched with the build command. For example, a target for the Windows platform with runtime v0.7.11 would be stored at ~/.lune/targets/0.7.11/base-windows-x86_64.exe, or one for M1 macs with runtime v0.8.0 could be stored at ~/.lune/targets/0.8.0/base-aarch64-macos.bin. These targets would be conditionally downloaded from the build artifacts published to GitHub releases when the build command for a particular target is invoked for the first time.

3. In case the user requests a target that lune doesn't provide precompiled binaries for, they can use the --base flag to provide a manually compiled lune binary for said target, which would then be patched.

[CompeyDev]

I've already started some work on this, just wanted to update here in case anyone was interested.