allow ComplexPattern % MonomerPattern
begin to implement __call__ on ComplexPattern
finished ComplexPattern.__call__
new exceptions used in ComplexPattern refinement
added support for bng "species" observables
raise exception if an initial condition pattern is unmatchable
refactor so core render can be called with an explicit species list
improve exception message for ComponentSet.index
start to implement an Expression class
finished initial Expression support
use inline-defined macros to access numpy arrays in rhs
fix test_model_pickle test failure by using _export=False
change ComponentSet repr to use components' repr instead of str

(fixes issue where components that now subclass sympy.Symbol were repr'ing
as just their name, which is Symbol's repr implementation)
fix some doctests that broke as a result of the Expression changes
renamed bng wiki sample models and switched egfr example to a more complex one
use more explicit sympy constructors rather than relying on sympify

(this fixed an issued where a parameter name like 'deg' would be interpreted
as a special function or the like, rather than a symbol)
make bng generator handle models with expressions but no parameters

(odd, but possible)