Shards subcommands

[White-Oak]

Implemented add <name> and remove <name>.

Currently, they add and remove 'features' from Cargo.toml of a project.

No tests, cause not sure how to test this. Maybe try to build a project?

This is an implementation of CLI task in Shards RFC.

[ebkalderon]

@White-Oak Hmm, it is too early to properly test this feature since we don't have a concrete implementation of the engine modules concept. Nor do we have any Cargo features in the engine to actually try, and we don't have a spec for zipped modules.

[White-Oak]

@ebkalderon It's a part one of "modules/shards" project, featuring "features".

[ebkalderon]

@White-Oak We should probably make an RFC for this, given the discussion we were all having on the general room. Implementing this properly might be an involved process.

[White-Oak]

@ebkalderon Certainly. But this is "the part one" as I mentioned erlier, so apart from naming it and naming commands it wouldn't have much alternatives (:

[White-Oak]

@ebkalderon if we agreed on CLI task in RFC for shards, this is ready to be merged.

[ebkalderon]

@White-Oak It looks like there are some conflicts with this pull request? Could you please resolve them? I think this is ready to be merged. We can keep discussing specifics on the shards RFC (amethyst/amethyst#34) and iterate on this as needed.

[White-Oak]

@ebkalderon sure! I'll do it asap

[White-Oak]

@ebkalderon Renamed modules to shards and used amethyst add <name> as a syntax.

[ebkalderon]

Sorry for the delayed response. I think this pull request is essentially done, despite our inability to effectively test it. I'll merge this now!