finish up #288, tested & documented
fix #287
add cy.renderTo()

@bumbu this is what you need

cy.renderTo( canvas2dcontext, zoom, pan)

idk if you'll need to set the pan but it's there if you need it :)
Added support for roundrectangle shape, including intersection calculations
Refs #297 Added Auriejir fix for bug relating to node border-width and background-image
refs #299 Added Auriejir's fix for bug relating to node background-image and 0 width node borders
Merge remote-tracking branch 'upstream/master'