fast_expf() solves known performance problem on x86_64
Add 'sharp-gaussian' filter
IBA make_kernel, convolve / oiiotool --kernel --convolve
oiiotool --blur
IBA::unsharp_mask and oiiotool --unsharp
Fix blur and unsharp tests -- lossy jpg is unreliable cross-platform
for exact comparisons.  Switch to lossless TIFF files.
Merge pull request #574 from lgritz/lg-convolve

Convolution, blur, unsharp mask.