Contains one function for drawing Piper diagrams (also called Piper-Hill diagrams) of water analyses for major ions.
added function testData to generate samples for creating piper objects
removed 'WaterType' and 'object' slots on piper objects because the concept was buggy. Better to assign pch and col parameters directly, example changed to reflect this.
fixed default pch and col assignment so more than 26 samples does not cause an error