regenerated xmobile backend

switch to vector text rendering in more cases

fixed text rendering test case

updated xmobile backend

fixed method order

changed the way window scaling is done

to support high DPI scaling, use the FramebufferSize functions in glfwcanvas and sdlcanvas to determine the canvas size

Merge pull request #22 from kanle-hotstar/bugfix/avoid-panic-when-loa…

…ding-image-cache

Fix a panic issue of loading an image from cache

GetImageData bugfix

fixed a bug with anticlockwise arcs and ellipses

updated to new sdl library version

tests should run on OpenGL backend

fixed a problem with closed paths and self intersecting polygons

added the readme example as a test