avoid duplicate file extensions

Merge branch 'nodoublefileextensions' of https://github.com/Chiamh/XChart into nodoublefileextensions

BUG-FIX Histogram

To avoid the tempMax problem

the tempMax should be -Double.MAX_VALUE, not Double.MIN_VALUE

Improved class Histogram

1. Improved the constructor. Now it has better performance when data is
vary large (e.g. >1M).
2. Fixed line 99. When bin==numBins, the value falls on the next bin of
the max bin, not right on the edge.

Allow tilting of X-Axis labels