Support passing "enum" values when using libffi
Support passing "enum" values when using libffi

This makes it possible to pass values of "enum" from Lua to C (and back) by
handling ERIS_TYPE_ENUM in eris_fcall_ffi_map_type(), which maps ErisTypeInfo
to ffi_type* values.

aperezdc/lua-eol,aperezdc/eris,aperezdc/eris,aperezdc/lua-eol