Fix for Swift and more flexible tint

Two commits here, the first prevents an issue with the Accelerate framework when importing FXBlurView into the Swift bridging header, the second provides more flexibility defining a tint colour.  I'm not sure why you had a fixed tint alpha previously, but I needed to be able to alter the blend mode and alpha to get the effect I was looking for, so I removed the fixed alpha and added a blend mode property.  Merge as you wish.

Cheers!