Replace USE_SPECIFIERS by USES_VARIABLES
Allow record=number as a shorthand for record=[number] in StateMonitor
Put "iterate_all" information into the templates
Fix a remaining reference to "specifier"
Add a first implementation of subgroups -- no support in StateMonitor, Synapses, etc. yet, only getting/setting of state variables
Make StateMonitor Subgroup-aware
Test subgroups for both Python and weave
Add Subgroup-awareness to the Synapses class