Splotch

* Fixed bug with 'ins' variable in colorbar()

* Added weights to hist()
* Fixed bug where input parameters could only be given as lists, not other iterable types

* Added sampling to cornerplot() to subsample the input data into a thinned dataset for faster plotting
* The 'nsamples' and 'sample_type' parameters were added to control the use of this feature
* Removed 'sharex' and 'sharey' parameters as they were superfluous in cornerplot()

* Fixed bug in cornerplot() when columns given as groups in a numpy array

* cornerplot() now accepts groups of parameters, the 'columns' parameter can be given as a list of lists with each sublist corresponding to a set of parameters to be paired together
* Giving multiple groups will overplot corresponding parameters from each group on the same axis

* Fixed axline() issue when parameters parsed as an array rather than single number