Adding package dependency support

[RealA10N]

Different packages and targets should be able to depend on other targets from different packages.

Key features:

• Each target in a package should be able to specify its own dependencies
• Targets can depend on other targets from the same package. For example, the test target should be able to depend on build.

Dependencies should be provided using:

• A path to a local directory that contains a setup.litemake.toml file
• A URL to a .git repository (should also be able to provide a specific tag, commit SHA, or branch)
• A URL to an archive (.zip, .rar, .tar, .tar.gz)

I'm currently planning to implement those dependencies as static libraries that will be linked in compilation time, but in the future, we might add the option to compile the dependencies as DLLs.