Milestone 2.0

This will be a major revision of Brian, and introduce some minor backwards incompatibilities. We plan to strip out a lot of old stuff that has been replaced with better features, simplify the design of features we already have, and make it generally more coherent. This will include:

* using Synapses instead of Connection, which will be removed pending an assessment of acceptable performance. * using code generation (for Python/C++/GPU) as standard for all major Brian objects (NeuronGroup?, Synapses, Threshold, Reset, etc.)