Fixed up the new model examples to reflect the new implementation (no mention of process_input/output but I think that's a pretty advanced thing most models won't need to touch).  Fixed, I think, the documentation references that were failing
Renames custom_model_1d to just custom_model and moves it to modeling.core, in the process updating it to support creating custom N-dimensional models.  custom_model_1d is still kept for backward compat but will be deprecated.
Fixed doctest to work on Python 2.6