ENH: Experimental summary functions
ENH: model summary functions
ENH: summary_params use_t
ENH: summary_col regressor_order
bug
Add back info_dict usage
Summary_col: Mechnism for default model infos and overwrites per model type

Results can add a property `default_model_infos` to specify a info_dict,
which is taken as the default for that model. Same names are merged into
one row, even if two different models are compared in one summary_col
call.

To overwrite, info_dict can nest a model-specific info_dict under the name
of the model, which would then be used. If no such key is found in the
dict, then the complete info_dict is used.

Example:
`info_dict = {"N":..., "R2": ..., "OLS":{"R2":...}}` would not show
N for OLS regression models.
add documentation on new info_dict behaviour
BUG py26 compatibility OrderedDict,  2 pylint errors
TST: add smoke test for summary2
Merge pull request #965 from josef-pkt/vincent_summary2_rebased

Vincent summary2 rebased closes #915