ondrolexa/apsg: APSG 0.6.1 release

What's new in this release Stereogrid always use Euclidean norms as weights DefGrad properties e1, e2, e3 (natural principal strains) added DefGrad properties eoct, goct (octahedral strains) added DefrGrad from_ratios class method added DefGrad properties k, d, K, D (strain symmetries and intesities) added New class Ellipsoid added to work with ellipsoids FabricPLot renamed to VollmerPlot for consistency RamsayPlot, FlinnPlot and HsuPlot implemented All fabric plots have new path method accepting list of tensor