Super Cool Ad Manager Plugin, version 0.3

Formerly known as DoubleClick for WordPress, this release of Super Cool Ad Manager Plugin brings a Gutenberg block for placing ads directly in stories, plus a number of bug fixes and customizability improvements.

Thanks to WordPress.org user onlineforbusiness and GitHub users dbeniaminov and tienvooracht for their contributions to this release.

New features:

• Adds a Gutenberg Block for manual insertion of ads in posts. Pull request #82 for issue #70.
• Adds a PHP filter 'dfw_js_data', to allow modification of the window.dfw object before it's output on the page. Refactors widgets and blocks to draw all details needed from window.dfw instead of separately-enqueued JSON blobs. This should allow you to `setRequestNonPersonalizedAds. PR #81 for issue #63, with thanks to GitHub user tienvooracht for the idea.
• Tested up to WordPress 5.0-beta3

Changes and fixes:

• Rebrands from "DoubleClick for WordPress" to "Super Cool Ad Manager Plugin", because Google merged DoubleClick for Publishers into Google Ad Manager.
• Potentially-breaking changes: Renames a number of varibles from camelCase to snake_case in pull request #46 for Wordpress.com VIP compatibility. This includes renaming the global variable $DoubleClick to $doubleclick, and many of its properties from $DoubleClick->camelCase to $doubleclick->snake_case. If you modify this plugin's features via filters or actions, or if you call this plugin's functions and methods directly from your code,
• Updates to jquery.dfp.js version 2.4.2, adding setCentering support. PR #67 for issue #66
• Adds "Category" targeting on category archive. PR #72 for issue #61.
• Adds "Tag" targeting on tag archive. PR #74 for issue #29.
• Fixes a number of PHP warnings and errors, including issue #8 and issue #37 in PR #76 and issue #31 in PR #80.
• Fixes a targeting problem that occurred when wp_footer ran outside The Loop. PR #87 for this support topic.
• Removes 'single' page targeting from post-type archives and from static front pages. PR #72 for issue #61, thanks to GitHub user dbeniaminov.

Documentation updates:

• Adds "Ad unit" label to widget settings for the "Identifier" setting, to match Google's language. PR #73 for issue #26.
• Adds GitHub Pull Request template and Contributing guidelines files.
• Adds a plugin text domain: dfw. (PR #76)
• Adds the GPL2 license to the plugin header; this plugin has been GPL2 since 2015 but that wasn't marked in a WordPress-accessible way. (PR #76)
• Moves the documentation index file from docs/index.md to docs/readme.md in the GitHub repository, so that the Markdown will display to all who visit the docs directory. (PR #80)
• Moves plugin functions and files around within the plugin; see PR #72 for details.