Cache: Document and Release V2 of actions/cache

[joshmgross]

With the recent improvements made to the cache action, we'll be releasing a V2 version of this action.

What's New

• Added support for multiple paths (https://github.com/actions/cache/issues/16), glob patterns, and single file caches (https://github.com/actions/cache/issues/33)
• Increased performance and improved cache sizes using zstd for compression (https://github.com/actions/cache/issues/184). (Off for windows-latest hosted runner)
• Allowed caching for all events with a ref (https://github.com/actions/cache/issues/63)
  
  
  
  • See Events that trigger workflows for info on which events do not have a GITHUB_REF
  
  
• Created the @actions/cache npm package to allow other actions to utilize caching (https://github.com/actions/cache/issues/55)
• Added a best-effort step to delete the archive after extraction to reduces storage space (https://github.com/actions/cache/pull/209).

To Do

• [x] Update README to include a "What's New" section and info about upgrading to v2
• [x] Update examples to reference v2 and use multiple paths if possible
• [x] Update the help docs (Caching dependencies to speed up workflows to reference v2 (Tracked via an internal issue
• [x] Update the action.yml description for path to mention glob, multipath, and single file support. This should link to @actions/glob for glob pattern documentation
• [x] Update the toolkit cache package README to include a link to the cache action as example usage.
• [x] Change log https://github.com/github/releases/issues/835

[aiqiaoy]

v2.0.0 is now released!