Add missing "Rank and Percentile" function from Data Analysis Toolkit.
Please note that Libreoffice 4.3 adds following functions:
PERCENTILE.EXC, PERCENTILE.INC, PERCENTRANK.EXC, PERCENTRANK.INC, QUARTILE.EXC, QUARTILE.INC, RANK.EQ and RANK.AVG, MODE.SNGL, MODE.MULT, spreadsheet functions
So adding percentile or atleast quartile, multi modal values using these new upcoming functions will be very useful.
Priority highest is reserved for MABs, please see: https://wiki.documentfoundation.org/MAB on when a bug qualifies for that.
Thus keeping this on priority high.
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