1. Rationalise the test suite.
   - Extend it. ..Some
   - Non-Win32 cases (notably, how to find the C library for tests!). ...OK
   - Split into multiple files. ...OK
2. Signatures
   - Returning pointers to structures/arrays
   - Passing "out" and "in/out" style pointers to basic types
   - Memory management issues for returned values
3. Makefile
   - Better handling of the ffcall library (maybe automate the build?)
4. Functionality
   - Add support for structure passing/return (eg, div() function).
   - Add support for passing characters as "s" (eg, toupper() function).
   - Add tests for these.
5. Bugs
   - Consider FFI::call($atoi, 'cIp', "-97") (note the 'I' (unsigned) return
     type). This returns -97 (note the negative value!). Why?
