Adds support for generics in`derive-impl`

[gupnik]

As raised by @kianenigma in https://github.com/sam0x17/macro_magic/issues/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
}

[gupnik]

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

Created a PR with the fix in flite: https://github.com/kianenigma/flite/pull/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