add CompositeModel, support '+', '-', '*', '/' of models
a few more tweaks for CompositeModel
Ahh, 'components' must be a property
OrderedDict from CompositeModel.eval_components
format Name collision error to show all collisions
use operator module for CompositeModel
use prefix as default key for Model.eval_components(), and pass params!
use operator.truediv (needed for py3, thanks TravisCI!)
MAINT: if something has the __call__ attribute, then it is callable
improve repr string
add __truediv__ for python3 support
improved docs for model / CompositeModel
ENH: adding differential evolution as a fitting method
MAINT: include _differentialevolution.py in source, not present in scipy until 0.15
avoid adding dict keys and list
removed cruft
remove cruft
allow any operator function for CompositeModel
add convolution exmple using custom CompositeModel operator
add CompositeModel to __init__.py