neo/core pep8 cleanup
fix bug in irregularlysampledsignal __eq__
fix initialization of recordingchannelgroup channel_indexes and channel_names
fix neo.test.tools handling of some assert_array_equals corner cases
implement merge method in all relevant classes
fix attributes not being copied on mathematical operations
fix bug in eventarray __repr__ for python 3
add __repr__ to epocharray
improve unit tests for neo core
improve unittest coverage for neo core