Improve numerical stability, preserve alpha

The 'pow' function doesn't work on negative values, so you should call saturate first.
Also made it preserve the alpha channel, can't think of a good reason why you shouldn't do so.
Merge pull request #16 from Shiandow/patch-1

Improve numerical stability, preserve alpha
Merged (manual) from Shiandow's ChromaScaler work branch with changes to ConfigDialog.
Merge pull request #17 from zachsaw/work

Added Shiandow's ChromaScaler render script
Fixed:
Filter.Append was reusing 'this' instance when clone was required causing blank screen to be displayed in some situations when input / output size changes.

Refactoring:
Pulled ConfigurableRenderScript.cs from Shiandow's experimental branch.
Refactored all relevant scripts to inherit from ConfigurableRenderScript class.
Fixed Filter.Append crashing out with stack overflow in some situations.
Added example of InterlaceFlags usage in MyRenderScript.cs.
Merge pull request #18 from zachsaw/work

Pulled from work branch
Added ability to specify up and down scalers in Resizer.Create().
Implemented workaround for config dialogs not showing in Visual Studio form designer.
Merge pull request #19 from zachsaw/work

Pulled from work branch
Make LoadSettings(), SaveSettings() abstract.
Reorder RenderScript class

Tried separating the parts that should be override from the parts that
do the actual work and the part that provides convenient functions.