Problem: renaming types at the C header layer is not possible

[danielhenrymantilla]

Support renaming the types (at the C header layer) for:

• Opaque types.

  • Syntax: #[ReprC::opaque("name_in_the_c_header")]

• everything else

  • Idea of the syntax: #[ReprC::rename("name_in_the_c_header")]

    • would probably override the syntax for opaque types for the sake of consistency

    • #[derive_ReprC(rename = "...")] would also be possible, but the ::syn-less equivalent of the ReprC! { ... } macro would then be left out.

[danielhenrymantilla]

Completed as per the latest safer-ffi changes. Demo:

• safer_ffi/ffi_tests/src/lib.rs

  Line 175 in c7c410e

  #[derive_ReprC(rename = "next_generation")]

• safer_ffi/ffi_tests/generated.h

  Lines 67 to 77 in c7c410e

  	typedef struct next_generation {
  	/** \brief
  	* I test some `gen`-eration.
  	*/
  	Bar_t gen;
  	/** \brief
  	* with function pointers and everything!
  	*/
  	void * (*cb)(bool);
  	} next_generation_t;

TODO: release to crates.io