BEP-4: Simplifying Brian
Abstract: This BEP proposes to simplify Brian's code by moving some classes to an "obsolete"
folder.

In order to make the code more readable and also to simplify the syntax of Brian, I propose
a number of simplifications. Removed classes should be put in an "obsolete" folder so as to
keep backward compatibility while simplifying the code. A "deprecated" warning could be raised
when those classes are used (see http://seewhatever.de/blog/?p=161).

First, the standard structure of a model is
equations + threshold + reset,
where the threshold is a Python expression evaluating to a boolean
and reset a series of Python statements.

Threshold
---------
StringThreshold should be the standard mechanism. Obsolete classes:
* NoThreshold
* FunThreshold
* SimpleFunThreshold
* VariableThreshold

PoissonThreshold and EmpiricalThreshold could also be replaced by or supplemented
with versions with expressions,
where PoissonThreshold expressions should return a vector of 0..1 values.

Reset
-----
StringReset should be the standard mechanism. Obsolete classes:
* VariableReset
* FunReset
* NoReset

Model
-----
Is the Model class really useful? (neuronmodel module)

quantityarray
-------------
We could move it the obsolete folder.