Slightly faster version of resize2.js available

Rescaling with bilinear, bicubic, bezier and hermite interpolation is a bit slow. I'm using a copy of `resize2.js` in my own [icon generator](https://github.com/idesis-gmbh/png2icons) and refactored it. I inlined all functions which sometimes got called for every single pixel. This speeds up rescaling a bit. Feel free to use this version [`resize3.js`](https://github.com/idesis-gmbh/png2icons/blob/master/lib/resize3.js) which is otherwise identical to the original `resize2.js` (apart from the removal of the `options` parameter which was never used).

There is also [`resize4.js`](https://github.com/idesis-gmbh/png2icons/blob/master/lib/resize4.js) with an alternative bicubic implementation that is much faster. The limitation of this version is that source and target image must have the same width/height ratio.