rrd4j 3.0 is out

[Fabrice Bacchella]

rrd4j 3.0 is out and available through maven repo.

It an important release that add many new features.

Dropped support for Java 6.
Removed gradle and ant build.
Improved the RPN calculator performance.
Added support for VDEF like datasources. They are functions that take a datasource and output a single value. They can be user defined by implementing the abstract
class org.rrd4j.data.Variable. A Variable class return a Value that can contain both a numerical value and a time stamp ; it's useful for functions like Max
that can return both an maximum value and when it occurred. They deprecated old aggregation functions.
More precise font selection, with more configurable elements.
gprint can take any previously defined datasource that is a defined from a Variable.
Line, vrule and hrule can be defined using a java's Stroke, not just a float width.
Line and Area can be stacked at will, without the needs of a stack.


And of course bug fix.