Splotch

* Various changes to plots_1d.hist() function:
* hist() now accepts the orientation parameter, which acts like matplotlib's orientation.
* changed the way colors are handled between the various hist_types such that the user does not necessarily need to switch between 'color' and 'edgecolor' when changing hist_types.
* Added autolimits on x/y axes depending on orientation
* Created step_fillerx function in base_funcs(), although, one could rework add an orientation parameter to original step_filler() function to achieve the same.
* Cleaned up several functions with pep-8

* Added scicm as the default colour map package for splotch

* Added weights to plots_2d.hist2D. Fixed the same normalisation issue that plots_1d.hist had, of calculating the density using all data points, not only those in the bin ranges.

* Fixed bug in plots_1d.hist that resulted in inaccurate results when 1) the bins spanned only a fraction of the total data range, 2) dens=True, and 3) scale!=None

* Made changes to contourp, contour and colorbar
* Changed plabel --> labels for consistency with other functions
* Default is to always return QuadContourSet from contour functions. If output=True, this appends the X, Y and Z.T hitogram bins to the return. Returning the result of the matplotlib contour functions is required in order for colorbar to act on a contour function.
* Made some changes to documentation and did some pep-8 linting

* Made some adjustments to colorbar() for easier usage
* Applied some pep-8 linting to some functions in axis_plots.py