Started (re)writing the equations docs
Start a separation between user and developer documentation
add some content to developer docs about namespaces
started implementation of explicit Namespace class
started work on making NeuronGroup work with the new namespace system
Simplify Equations/CodeStrings to be simple convenience wrappers, not
saving any namespace (for now, unit checking is not implemented)
Move stuff around, rename CompoundNamespace to ModelNamespace and adapt
to the new Equations objects
Implement "replacements by keyword" in Equations
Convert scalar quantities to float instead of 0-dim numpy arrays when
stripping away units
Do not use SyntaxError (error messages will not work in ipython)
A lot of changes to make it work again with all the namespace/equations
changes. The example at the end of the file should work again (both with
Python and with C++).
Add an OrderedDict backport to not lose compatibility with Python 2.6
update documentation
small change to the create_namespace method, add more thorough testing
for namespaces.
Do not allow changes to the namespace object
Shift everything around, move some responsibility to codegen (only
Python works for now)
Make CPP code generation work again with the new system
Merge master branch (with the new preferences system)

Conflicts:
	brian2/groups/neurongroup.py
Add a new property "identifiers", returning a set of all identifiers
used in the equations (except for variables defined in the equations).
Make get_identifiers return a set instead of a list.