README: Add jQuery environment notes
Docs: Link to the browser support page in CONTRIBUTING.md

Instead of duplicating the supported browsers matrix, just link to
the browser support page on jquery.com.
Effects: First step() call should match :animated selector

Fixes #14623
Closes gh-1473
Build: Happy New Year! Thanks @marlonlandaverde
Intro: Pass window to intro if available, for browserify

Closes gh-1476
Tests: Remove html5 shiv
Release: Publish to npm

Closes gh-1479
Authors: Update AUTHORS.txt and .mailmap
Selector: Update Sizzle

Fixes #14657
Sizzle: update committed dependencies
Tests: Remove one of the checks for memory leak

This check is redundant since jQuery.fragments object does not exist anymore
Attrs: Remove outdated valHook for option element

This hook was relevant for BlackBerry 4.7 which is no longer supported.

But this code path now raises error in IE10-11 (#14686) in 1.x-master branch.
So to just to be safe, also add test for IE issue to this branch too.
Tests: Add assertion for the jQuery#val method
Tests: Fix code style issues
Traversing: Check all pairwise element combinations for .find( els )

Ref b8d0d54a3c4960794a1b492957abeb56eddd1e48
Fixes #14701