Release of version 0.71

The release 0.71 of JSXGraph contains major improvements of ticks on lines. Equidistant and special ticks are possible now. Further it contains much improved automatic labeling of axes, see for a description. The snap-to-grid mode has been enabled again. Further the release contains many bug fixes, among them the fix of a problem with lines and curves having points far outside of the drawing panel. The JSXGraph plugins for WordPress, Moodle and MediaWiki have been improved. The demo wiki contains many new examples.