Meta: Move loading logic into each feature (#1694)

- Move loading logic (`when`, `where`) near the feature's code instead of being listed in 3 separate functions (`init`, `onDomReady`, `ajaxedPagesHandler`) in a different file (`content.js`)
- Avoids the messy content.js list of imports/uselessFunctionNames by halving the file length
- Enables us to actually list all the features in Options (not part of this PR) since they are _all_ added in `feature.add('feature-name')` on load

contributing.md

@@ -8,11 +8,63 @@ Suggestions and pull requests are highly encouraged! Have a look at the [open is
 - The extension can be loaded into Chrome or Firefox manually ([See notes below](#loading-into-the-browser))
 - [JSX](https://reactjs.org/docs/introducing-jsx.html) is used to create DOM elements.
 - All the [latest DOM APIs](https://github.com/WebReflection/dom4#features) and JavaScript features are available because the extension only has to work in the latest Chrome and Firefox. 🎉
-- Each JavaScript feature lives in its own file under [`source/features`](https://github.com/sindresorhus/refined-github/tree/master/source/features) and it's loaded on condition in [`source/content.js`](https://github.com/sindresorhus/refined-github/blob/master/source/content.js).
-- Some GitHub pages are loaded via AJAX/PJAX, so some features need to be in the special `ajaxedPagesHandler` function (see it as a custom "on DOM ready").
-- See what a _feature_ [looks like](https://github.com/sindresorhus/refined-github/blob/master/source/features/add-time-machine-links-to-comments.js) and [how it's loaded](https://github.com/sindresorhus/refined-github/blob/d7768508c3919558daa6b2ccc5a15aa73d081551/source/content.js#L176) (in this case it uses `observeEl` to automatically be run when new comments are loaded via AJAX)
+- Each JavaScript feature lives in its own file under [`source/features`](https://github.com/sindresorhus/refined-github/tree/master/source/features) and it's imported in [`source/content.js`](https://github.com/sindresorhus/refined-github/blob/master/source/content.js).
+- Some GitHub pages are loaded via AJAX/PJAX, so some features use the special `onAjaxedPages` loader (see it as a custom "on DOM ready").
+- See what a _feature_ [looks like](https://github.com/sindresorhus/refined-github/blob/master/source/features/user-profile-follower-badge.js).
 - If you're making changes to the README, try to match the style of the content that's already there and when in doubt, take a look at [our little style guide](https://github.com/sindresorhus/refined-github/issues/1139).
 
+## `features.add`
+
+The simplest usage of `feature.add` is the following. This will be run instantly on all page-loads (but not on ajax loads):
+
+```js
+import features from '../libs/features';
+
+function init () {
+	console.log('✨');
+}
+
+features.add({
+	id: 'make-github-more-refined',
+	init
+});
+```
+
+Here's an example using all of the possible `feature.add` options:
+
+
+```js
+import select from 'select-dom';
+import features from '../libs/features';
+
+function log() {
+	console.log('✨');
+}
+function init() {
+	select('.btn').addEventListener('click', log);
+}
+function deinit() {
+	select('.btn').removeEventListener('load', log);
+}
+
+features.add({
+	id: 'make-github-more-refined',
+	include: [
+		features.isUserProfile,
+		features.isOrganization
+	],
+	exclude: [
+		features.isOwnUserProfile
+	],
+	load: features.domReady, // Wait for dom-ready
+	// load: features.onAjaxedPages, // Or: Wait for dom-ready AND run on all ajaxed loads
+	// load: features.onNewComments, // Or: Wait for dom-ready AND run on all ajaxed loads AND watch for new comments
+	deinit, // Rarely needed
+	init
+});
+```
+
+
 ## Workflow
 
 First clone:

package.json

@@ -20,12 +20,12 @@
 		"dom-chef": "^3.2.0",
 		"dom-loaded": "^1.0.1",
 		"element-ready": "^3.0.0",
-		"github-injection": "^1.0.1",
 		"github-reserved-names": "^1.1.4",
 		"intervalometer": "^1.0.4",
 		"linkify-issues": "^1.3.0",
 		"linkify-urls": "^2.2.0",
 		"onetime": "^2.0.1",
+		"p-is-promise": "^2.0.0",
 		"select-dom": "^4.1.3",
 		"shorten-repo-url": "^1.5.0",
 		"storm-textarea": "2.0.1",