Prevent divide by zero for a constant image
Add test for constant data
Add missing asinh to scale_image
Add test for asinh in scale_image
Add asinh to fits2bitmap
Merge pull request #38 from larrybradley/constantimage

Prevent divide by zero when normalizing a constant image
Merge pull request #39 from larrybradley/asinh

Add missing asinh option to scale_image and fits2bitmap script
Fix for #40 and #29
Fix for #31