Veusz 2.999 (testing version)

This is testing version of 3.0 which includes the brand new 3D support.

• New 3D support for plotting points, functions, surfaces and volumes
• Add --export-option parameter for command line exporting control
• Add templates in preferences for exported file names, add %PAGE00% and %PAGE000% options for zero-prefixed page numbers, and change %PAGENUM% to %PAGE%
• In export dialog allow user to specify arbitrary pages to export
• Change miter limit for lines, which fixes some problems when exporting arrow to PDFs
• Use flat cap on lines with arrows, to avoid line showing through head
• Support datetime64 and string/unicode characters in npy/npz import
• Add \hat LaTeX support