genn-team/genn: GeNN 3.1.1

This release fixes several small bugs found in GeNN 3.1.0 and implements some small features: User Side Changes Added new synapse matrix types SPARSE_GLOBALG_INDIVIDUAL_PSM, DENSE_GLOBALG_INDIVIDUAL_PSM and BITMASK_GLOBALG_INDIVIDUAL_PSM to handle case where synapses with no individual state have a postsynaptic model with state variables e.g. an alpha synapse. Bug fixes: Correctly handle aliases which refer to other aliases in SpineML models Fixed issues with presynaptically parallelised synapse populations where the postsynaptic population is small enough for input to be accumulated in shared memor