Implement scm_c_define_gsubr high-level binds

[Javyre]

This will probably require another proc_macro_hack macro for detecting parameter types and generating a proper proxy C func...

[Javyre]

Roadmap:

• Main parser code
• Required arguments
• Optional arguments
• Foreign object support in arguments
• Whatever the rst argument in scm_c_define_gsubr means

[Javyre]

So apparently the rst parameter is explained on the GNU/MIT/Scheme reference
I'm not 100% sure but this could be the explanation.

gnu documentation