Merge pull request #73 from brian-team/boolean_parameters

Allow for boolean state variables. Closes #68
Allow creating synapses without model equations
Add another test for the Synapses class
Merge remote-tracking branch 'origin/master' into synapses
Switch explicit state updaters to the new "x_new = ..." Syntax we agreed upon
Fix an issue with the not_refractory variable not correctly identified as boolean
Nicer output for unitless variables
Rename the equations keyword argument to model (as in Brian 1)
More tests for the Synapses class
Don't use .format syntax that is not Python 2.6 compatible
Yet another test for the Synapses class
Remove the "N" argument for create_namespace
Remove outdated documentation and examples
More debug logging and more verbose assertion failure (to figure out why the tests are currently failing on travis)
New directory structure for languages, doesn't run yet.
Languages working now, just need to get runtime and codeobject working
Make linear state updates work with sympy 0.7.3
...but not at the cost of breaking it for 0.7.2
Finished refactoring languages into languages+runtime, added preferences
Fixes for Synapses