statistics: initial value for 'max' statistic set to -std::numeric_limits::max().

As std::numeric_limits::min is minimum positive normalized value for floating types.
And std::numeric_limits::lowest is C++11 feature which is not widely supported.
LGPL3 licensing.
build/ directory added to .gitignore
Handystats changelog added (CHANGES.rst).
debian: combaine-plugin-handystats package removed.
Version bump 2.0.0