Add event.relatedTarget + `data-*` example to Modal docs

Fixes #14245

Add Wall of Browser Bugs entry for #14972

Fix typo

Corrected spelling of the word "elements"

fix whitespace in js dropdown docs

Update Jekyll to v2.4.0 and rouge to v1.7.2.

Examples: Make use of the `footer` tag instead of a class.

Cover common contributor mistakes in CONTRIBUTING.md

Based on https://github.com/twbs/rorschach/tree/master/docs

Add Wall of Browser Bugs entry for #14409

Closes #14409.
[skip sauce]

Explain issue/PR bots in CONTRIBUTING.md

Customizer: listen to the right event for manual file selection in import

This reverts commit ea239691.

BootstrapCDN has now uploaded Bootstrap v3.3.0

Replace deprecated uses of .pull-left & .pull-right in .media docs

[skip sauce]
[skip validator]

Refs https://github.com/twbs/bootlint/pull/153
[skip sauce]

Closes #14941

Fix the iOS 8 unit test failures

Resolves #14919.

Use jsDelivr CDN until BootstrapCDN gets updated

Use RegExp for button plugin's focus shim

Fixes #14923.

Add Wall of Browser Bugs entry for #14708

Closes #14708

Add Wall of Browser Bugs entry for #14868

Closes #14868

Conflicts:
	docs/assets/js/customize.min.js
	docs/assets/js/raw-files.min.js