Stats: added CSPL_Stats_median_quickselect()
Stats: added tests for CSPL_Stats_median_quickselect()
Special: minor cleanup in erf
Array: added CSPL_Array_linspace(), CSPL_Array_sum(), CSPL_Array_suml()
Stats: added a median funciton that will allow for additions to the data in chuncks, CSPL_Stats_median_bin()
Tests: update cmake to build the median tests