Gaussian refactor

Thing what was broken:

1. Radius was not actual radius, it was actually diameter. So compared with other implementations it had to be multiplied by 2. I saw comment about it was fixed, but it don't.
2. Float radius realization was awful. It did rounding radius then devided extreme coefficients. This is meaningless because with changing radius all coefficients should be restated. Again, this was marked as fixed but not.
3. Working window was hardcoded and was too narrow. Only 2*radius, what led to artifacts in some images. To be clear, this is Gaussian with radius of 5.
![screen shot 2014-10-12 at 1 43 45](https://cloud.githubusercontent.com/assets/128982/4604529/cfe3f61a-51a4-11e4-8039-aa6e5eed6bc7.png)
Vertical lines is 1x window, 2x and 3x (5, 10 and 15). 2x window is obviously truncates significant part of pixel value. Now this scale can be tuned with `effectiveScale` float argument. Default is 2.6x.

I don't like name `effectiveScale `, but I can't think of anything more appropriate. This commits are on top of my other pull request.