Export libffi type symbols.
Simplify toplevel funcs: dlopen -> load, dlsym -> sym.
Report load()/sym() not found errors properly.
Support specifying param types both as char codes and FFI types.

Return type need to be specified as string so far (need some special
values, like, string).
More type char codes.
Pass integer args properly.
Rename test to signify that this uses arg types encoded as char codes.
Add sqstd_getblob().