Adds support for generics inderive-impl

[gupnik]

As raised by @kianenigma in sam0x17/macro_magic#15, this PR adds the support for generics while using derive_impl.

This can then be used in conjunction with FliteFrameSystem being defined here as

+#[derive_impl(FliteFrameSystem<Configuration>)]
impl frame_system::Config for Runtime {
  type Block = Block;

  // .. Rest can be removed
}

[kianenigma]

Cool! can we have a e2e-ish example in our repo as well?

Else, can you see if you can fix flite/runtime using this?

It should be fairly easy to update the dependencies to this PR's last commit, given that we use the umbrella crate there :)

[gupnik]

Else, can you see if you can fix flite/runtime using this?

Created a PR with the fix in flite: kianenigma/flite#1

[franciscoaguirre]

This is going to be insanely useful 🚀

[kianenigma]

This is going to be insanely useful 🚀

wen XCMLite? :D

[franciscoaguirre]

This is going to be insanely useful 🚀

wen XCMLite? :D

On it now :D