Added c interop package to godropbox

This allows a multithreaded C or C++ program to call a goroutine and multiplexes the input and output streams
When Read encounters an error or end-of-file condition after successfully reading n > 0 bytes, it returns the number of bytes read. It may return the (non-nil) error from the same call or return the error (and n == 0) from a subsequent call.

This seems to indicate I should handle errors with some size attached