Release v0.24.0

-        gr3: Added gr3_drawtrianglesurface()
-        gr3: Use 256 color GR colormaps in gr3_convenience.c
-         gr: added tricontour() function
              Contouring for unstructured 2D triangular meshes
-         gr: take respect of Matplotlib's new dpi setting
-         gr: corrected color maps
-         gr: fixed unicode bug
-    gr/pygr: fix issues with adjusting range
- pygr, qtgr: Fix mouse events possibly return wrong x, y values.
-  pygr/mlab: Fixed a bug in the contourf() function
-       qtgr: fix memory leak in GRWidget.
-      gksqt: improved Qt application (gksqt)
-      gksqt: improved ROI selection logic
-        gks: fixed a Free Pascal problem
-        gks: use correct dpi settings
-        gks: fix a Qt performance issue
-        gks: improved nominal marker size / linewidth
-        gks: improved error handling
-        gks: improved memory management