vgx11: first import from github.com/Arrow/vgximg
vgx11: migrate to github.com/gonum/plot. rename package to vgx11
vgx11: vg.Inches is gone
vgx11: reduce stutter. (XImgCanvas->Canvas, XimgPainter->Painter)
vgx11: fixup inches (double) conversion
vgx11: add example
vgx11: package doc
vgx11: add not-windows build constraints
vgx11: add license for code from freetype-go
vgimg: add NewImageWithContext to use a user-provided GraphicContext
vgx11: embed vgimg.Canvas
vgx11: remove dup-code from vgimg
vgx11: remove stale comment
Merge pull request #3 from sbinet/dev-vg-x11

add an X11 vg back-end
vg/vgl: first stab at an opengl vg backend