build 2.3.x branch on travis
travis: run tests
iwyu
optimize webp pixel copy by moving row chunks rather than pixels - refs #2024
optimize case where image_view is used but is not a subset - refs #2024
remove debug prints
add missing colorize-alpha changelog entry - refs #1371
fix image-filter serialization for scale-hsla and colorize-alpha
add link to SVG gradient stops in colorize-alpha notes
move colorize-alpha to visual test suite - refs #1371
another colorize-alpha test - this one likely exposing a bug - refs #1371
protect against invalid memory access if agg gradient lookup fails to build
fixed test images after f4c3620d67
allow single color colorize-alpha
fix code formatting
skip webp tests that cannot run because expected test images cannot be opened - avoids 'WebPGetInfo failed' error
catch one more case of webp needing test workaround for old systems
gah, completely disable image comparions for webp since versions differ too widely
+ avoid copying feature_ptr during r-tree initialisation + avoid taking reference to temporary
merge with branch 2.3.x