[Feature] rocks.loader to support multiple dependencies with different versions

[mrcjkb]

thought: we're going to have to implement an equivalent to the luarocks loader to support multiple versions of the same dependency.
And for people who don't have the loader enabled, we might want to consider adding a flag that disallows conflicting dependencies. Which would mean we'll need a more sophisticated dependency resolution.

Originally posted by @mrcjkb in #74 (comment)