cffi: do benchmarks against CCL and SBCL

eventually introduce back static inline for compiled in cffi.

with-backend

• document *cffi-ecl-method* in cffi.
• benchmark two methods in cffi.
• check if cl-opengl may perform better with ECL and let know |3b|.

static ffi has problems due to a loose external dependency declarations (i.e all pointers are declared as void *) - so if we have the previous (exact) declaration in includes, it makes the compilation fail. See CFFI tests.

changed milestone to %ECL 16.2.0