force pixel aspect ratio to 1.0 if zero denominator to avoid PAR of NaN
Fix bug in IBA::circular_shift -- negative shifts didn't wrap correctly
ImageBufAlgo::polar_to_complex and complex_to_polar, oiiotool --polar and --unpolar

These convert between polar (amplitude, phase) and complex (real, imaginary)
representations of frequency-space data.
CHANGES and other minor docs fixes
Have PNG output respond properly to 'oiio:UnassociatedAlpha' request
Adds support for Nuke-style %V and %v wildcards to oiiotool.
Default views are "left" and "right", but these may be overridden with --views.