* Upgrade FontAwesome to 5.3.1
- Upgrades FontAwesome to a new major (breaking) version, but
is backwards compatible because we include the v4-shims CSS that maps
old names to new.
- This is a step toward full V5 adoption that doesn't require us to
come up with a plan for deprecating V4 icon names.
- Details: https://fontawesome.com/how-to-use/on-the-web/setup/upgrading-from-version-4
- Related to #2156 and #1966
* Improvements to icon
- Clarify in docs that fontawesome V5 icons accessible with V4-style names
- Make icons browseable: icon('address-book') will now open the Viewer
pane of RStudio IDE so that icons can be experimented with more easily.
* Update LICENSE with CC for FontAwesome .svgs
* Update NEWS