Depends on #904.
Add BackgroundColor, BorderColor, BorderWidth, CornerRadius and Padding
properties.
Modularize button painting code.
Paint border after background to get slightly better border appearance.
Update screenshots.
Add screenshot test using properties.
This change is done very carefully to minimize the number of changed
files, and use almost only file renames.
This is both for avoiding merge conflicts, keeping file history
unbroken, and keeping the PR easy to review.
A future PR will rename masonry to masonry_core, masonry_winit to
masonry change all the doc tests and snapshots that depend on those
names, etc.
After *that*, future PRs will have actual code changes splitting winit
away from masonry_core.
Olivier FAURE