Update README and compatible versions.
improve refresh time by taking load time into account
Add different vertical-alignment options, with larger thumbnails in icons+thumbnails mode

Avoid recreating thumbnail holder.
Center all thumbnails.
Remove thumbnail indicators.
And many more improvements.
ensure that some things live on even if we are disabled
let F6 switch through the available vertical-alignment types.
Add optional thumbnail headers (not displayed in center alignment), toggled with F7.
refactoring: some renaming
make the entire thumbnail holder sensitive to mouse clicks, not only the thumbnail
make more variables persist through a disable/re-enable cycle.
Urgent-window handling: don't highlight entire item, only the icon.
use a changed-handler for the alt-tab style gsetting.
enable live switching between the most common alt-tab styles by pressing F8.
F9 switches between the different thumbnail-behind-icon styles.
make origin-indicator arrow optional (no UI for toggling it though)