Percentile: Bug fixes and compliance with Excel.

High boundary check for percentile was against 100, should be 1.0.
Close to 0 (like 0.01) or 1 (like 0.99) percentile values for Nist and Interpolation methods
caused array out of bounds exceptions.
Seemingly arbitrary small dataset restriction removed.
Out of range percentile values and empty dataset return double.NaN
instead of throwing, similar to Excel returning #NUM! in such cases.