Ported to work with WiringPi

The plain GPIO version of librf24-rpi was modified to work with the
WiringPi library instead of the (custom?) compatibility layer. Very useful for individuals like me who wish to use both librf24-rpi and WiringPi, but previously couldn't due to incompatibilities. WiringPi was (pretty much) a drop-in replacement for the functions used in the GPIO version.