Document that alerts are removed from the DOM when closed; fixes #14318
bump grunt-autoprefixer to ~1.0.0
Merge pull request #14332 from hnrch02/clarify-alert-removal

Document that alerts are removed from the DOM when closed; fixes #14318
Merge pull request #14334 from twbs/update-autoprefixer

bump grunt-autoprefixer to ~1.0.0
Small wording tweak in alert docs
Make grunt concat js files when watching
Merge pull request #14336 from michaeljayt/patch-2

Make grunt concat js files when watching
Clean up buttons documentation
Merge pull request #14325 from hnrch02/cleanup-buttons-docs

Clean up buttons documentation
Gruntfile.js: Use user-friendly properties.
Gruntfile: switch cssmin & jade tasks from `files` over to `src` & `dest`

Refs #14388.
Merge upstream bootstrap commits