genn-team/genn: GeNN 3.1.0 RC

This release builds on the changes made in 3.0.0 to further streamline the process of building models with GeNN and includes several bug fixes for certain system configurations. User Side Changes Support for simulating models described using the SpineML model description language with GeNN. Neuron models can now sample from uniform, normal, exponential or log-normal distributions - these calls are translated to cuRAND when run on GPUs and calls to the C++11 library when run on CPU. Model state variables can now be initialised using small snippets of code run either on GPU or CPU. This can save significant amounts of initialisation time for large models. New MSBuild build system for Windows - makes developing user code from within Visual Studio much more streamlined. Bug fixes: Workaround for bug found in Glibc 2.23 and 2.24 which causes poor performance on some 64-bit Linux systems (namely on Ubuntu 16.04 LTS). Fixed bug encountered when using extra global variables in weight updates