ci: improve release process, clean up and re-org repo, add automated minification (#143)

* ci: update scripts

* release 2.7.1

* remove tracked stylesheets

* docs: revert stable tag to 2.7.0

* chore: move Plugin source into own dir

* docs: delete info texts

These can now be found in the [project wiki][wiki].

[wiki]: https://github.com/markcheret/footnotes/wiki

* docs: tweak contributing guide

* ci: reflect new directory structure

* chore: update gitignore

* chore: reflect new dir structure

* docs: update documentation

* build(linting): add Husky hooks, Markdown linting, lint all MD files

* fix pre-push command

* fix pre-push command

* build: add stylesheet, JS minification

* ci: add linting steps

* ci: comment out CSS linting step (that's going to be a whole *thing*)

* ci: minify all JS files

* ci: call correct JS file

* chore: lint

* ci: fix PHP linting commands

* chore: increment version constant string

* ci: concat AMP stylesheets

* ci: improve build scripts

* chore: add assets dir

src/templates/dashboard/settings-excerpts.html

@@ -0,0 +1,11 @@
+<table class="settings_excerpts widefat fixed">
+	<tbody>
+		<tr>
+			<td>[[label-excerpts]]</td>
+			<td>[[excerpts]] <span class="footnotes_notice">[[notice-excerpts]]</span></td>
+		</tr>
+	</tbody>
+</table>
+<div class="footnotes_description">
+	<p>[[description-excerpts]]</p>
+</div>