Some small changes mainly to documentation comments in files but also introducing "GeNNerror".
Updated documentation.
Merge branch 'development' of https://github.com/genn-team/genn into development
Updated documentation.
Fixed fatal bug in MBody1 project (cudaResetDevice was being called before freeMem, so freeMem was trying to clear variables that had already been cleared by ResetDevice).

Also fixed a freeMem() bug, where spike event arrays glbSpkEvnt were trying to be deleted twice.
Merge branch 'development' into nrn_var_que