Merge pull request #98 from halfflat/feature/sort-synapse-indices

src/fvm_multicell.hpp

src/util/range.hpp

src/util/rangeutil.hpp

src/util/sentinel.hpp

tests/global_communication/test_mpi_gather_all.cpp

tests/unit/test_cell_group.cpp

tests/unit/test_fvm.cpp

tests/unit/test_fvm_multi.cpp

tests/unit/test_probe.cpp

tests/unit/test_range.cpp

tests/validation/validate_soma.cpp

tests/validation/validate_synapses.cpp