bugfix for cy.fit() on empty graph causes invalid zoom & pan values => bad state
downloads don't open new tab
add cy.forceRender() for #388
clean up
fix #389
clean up zooming code and fix #386
document #283
refactor drawing a bit; cy.png() export now allows bg spec & (full image or current viewport); should fix flicker issue in navigator plugin; closes #378 with added documentation
document initrender & cy.json(); closes #328