BUG: Should return unicode not string.
ENH: Allow encoding for unicode.
Merge pull request #1983 from jseabold/fix-compat

BUG: Fix compat asunicode
created the function auto_plot, base for the facet_plot
created the function facet_plot
the formula definition of the plot is treated as a composition of patsy formulas
completed the formula interpretation, inserted the subset slicing of the dataframe
refactored the main function removing the code duplication and confusion
extended the code comments
use the violin plot instead of the boxplot when the exog is categorical
added the ellipse to the scatterplot
corrected a bug on the violinplot function call
autoplot is now a public API function to allow the user to leverage it on multiple subplots
improved the management of the subplots as location, distance sharing of axis and axis labeling
improvement in the management of the subplots
added a __plot__ hook for future usage on the autoplot function
inserted the possibility of optional graph type
perfected the implementation of the choice of plot, expanded the help
extended the docstrings of both autoplot and facet_plot, implementing boxplots and points for all combinations
added the plot types for the single variable plot and corrected the help