Feature/managed remove

Updated SVG and VML engines with new codes within `elproto.remove`, `paperproto.remove` and `paperproto.clear`.

- Added test case for checking whether element removal is actually dereferencing elements
- Added benchmark specs to check speed of paper removal

There has been about 20% decrease in performance of paper.remove and its related calls. However, no performance decrease has taken place for individual element removal (other than `.group`). The screenshot is comparison between this branch (top) and develop (below).

![screenshot 2014-02-20 19 28 29](https://f.cloud.github.com/assets/232373/2218890/c8fef9c8-9a37-11e3-92f9-de52746dbff0.png)


PS: Removed unwanted files from tests directory.