Summary re-write

TODO:

* [ ] Reverse name in call. Proper: def summary(self, yname=None, xname=None, title=None, alpha=.05, yname_list=None):
* [ ] Individual column alignment
* [x] More column spacing by default in summary_params
* [x] option to *not* enforce equal table width
* [ ] default lrlr alignment for model info panes
* [ ] summary_col: order/rename regressors in the row index


http://nbviewer.ipython.org/4124662/

What's in here: 

* Summary class: smry = Summary()
* Convert user input to DataFrames: smry.add_dict(), smry.add_df(), smry.add_array()
* DataFrame -> SimpleTables -> Output: smry.as_text(), smry.as_html(), smry.as_latex()
* Helper functions for convenient generation of summary objects: summary_params, summary_model
* Side-by-side summaries for multiple models: summary_cols
* 14 tests
* The main model summaries have all been converted to the new format. I've kept the old summary functions as "summary_old.py" so that sandbox examples can still use it in the interim until everything is converted over. 

On ASCII tables implementation: _measure_tables takes a list of DFs, converts them to ascii tables, measures their widths, and calculates how much white space to add to each of them so they all have same width. Then, smry.as_text() produces a new set of ascii tables via SimpleTable by specifying the white space in the colsep output option. In theory, this means we shouldn't ever have to fiddle with make tables fit by hand, and larger column titles/entries should be accommodated (within reason). 

PS: The test failure that currently makes Travis go red is trivial to fix.