v0.21.2 - 13th January 2019

• Ensure all metadata is removed from PNG output unless withMetadata used.

• Ensure shortest edge is at least one pixel after resizing. #1003

• Add ensureAlpha operation to add an alpha channel, if missing. #1153

• Expose pages and pageHeight metadata for multi-page input images. #1205

• Expose PNG output options requiring libimagequant. #1484

• Expose underlying error message for invalid input. #1505

• Prevent mutatation of options passed to jpeg. #1516

• Ensure forced output format applied correctly when output chaining. #1528