Lazy Rendering Introduction

• Introduces an opt-in for lazy rendering of tooltips and popovers (#104)
• adds lazy-rendering documentation to the README (c41ff9a) and (https://github.com/sir-dunxalot/ember-tooltips#240-release)
• each instance in the demo page uses lazy-rendering (http://sir-dunxalot.github.io/ember-tooltips/)

Lazy-rendering will improve load time for pages with many tooltips and popovers. Tooltip and popovers are only inserted into the dom and rendered when the user interacts with the tooltip/popover target with a click, mouseover, or focusin. To enable this improvements add the enableLazyRendering=true flag to your components.

enableLazyRendering=true will be the default behavior in release 3.0.0