correction in model.__add__ method, so we can deal with the case single_model + composite_model
FIX: Detects scalar indep vars properly; also accept Python lists.
FIX: Broadcast a constant result in model.eval()
Merge pull request #125 from licode/model_sum

correction in model.__add__ method
allow IPython version < 2 to not try to load widgets
cleaned up flow in Model.__add__()
updated Thanks file
Merge pull request #126 from danielballan/scalars-and-list

Scalars and list
Merge pull request #128 from newville/master

Cleanup of Model.__add__() + two bug fixes
Add tests for composite models __add__
Merge pull request #129 from tritemio/comp_models_add_tests

Add tests for composite models __add__
FIX: Use asfarray on data and indep vars if needed.
TST: Add a test using None
REF: Organize Fitter file structure.
Merge pull request #130 from danielballan/asfarray

FIX: Use asfarray on data and indep vars if needed.
more doc tweaks
more doc tweaks
remove old wrapping and models
move fitter.py to ui/basefitter.py, update imports
import Fitter from ui in __init__.py