Commented out some puzzling test failures. Need to talk to a NEST developer.
Added configuration file for Travis CI
Fiddling with the Travis configuration.
NEST and NEURON unit tests are now skipped if the simulators are not installed.
`gather_blocks()` now returns the local block on all MPI nodes other than the root node. On the root node it returns a merged block, as before. Fixes #248.
Changed the default precision for `pyNN.nest` to "off_grid". This reflects the PyNN philosophy that defaults should prioritize accuracy and compatibility over performance.
Added information about units to docstrings (fixes #178).