v0.7.0

- Supports zoom (#1, #79) and rotate(#81).
- Add 2 new options: "zoomable" and "rotatable".
- Add 6 new methods: "enable", "disable", "zoom", "rotate", "getDataURL"
(#80) and "setDragMode".
- Rename "release" method to "clear".
- Rename "setImgSrc" method to "replace".
- Rename "getImgInfo" method to "getImageData".
- Some other improvements.