genn-team/genn: Service release 2.2.3

This release includes minor new features and several bug fixes for certain system configurations. User Side Changes Transitioned feature tests to use Google Test framework. Added support for CUDA shader model 6.X Bug fixes: Fixed problem using GeNN on systems running 32-bit Linux kernels on a 64-bit architecture (Nvidia Jetson modules running old software for example). Fixed problem linking against CUDA on Mac OS X El Capitan due to SIP (System Integrity Protection). Fixed problems with support code relating to its scope and usage in spike-like event threshold code. Disabled use of C++ regular expressions on older versions of GCC. Please refer to the full documentation for further details, tutorials and complete code documentation