Add tests for gen_challenge() and test_answer()

Closes GH-632.

Fix mousetrap.js (#655)

Add Longhorn PHP 2022 CFP announcement

Closes GH-654.

Update mousetrap.min.js

Upgrade hogan.js

Delete jquery.ui.totop.js

UItoTop was dead script since https://github.com/php/web-php/commit/613a15b4954034a65072cd78d007072221779998

Update jquery.scrollTo.min.js

Move jquery.scrollTo.min.js to a new file

Update footer.inc

Drop IE support including IE 7 & 9 shims

Update jQuery from 1.10 to 3.6

Drop Modernizr (#653)

We only used it to check for data: URI support, but that's universally supported now https://caniuse.com/datauri

Fix: Avoid generating code without space between comma and function argument

Closes GH-650.

Fix: Replace weird comment with DocBlock

Closes GH-649.

Enhancement: Enable `no_extra_blank_lines` fixer

Closes GH-646.

Enhancement: Enable `line_ending` fixer

Closes GH-645.

Enhancement: Enable `trim_array_spaces` fixer

Closes GH-644.

Enhancement: Enable `ordered_class_elements` fixer

Closes GH-641.

Enhancement: Enable `array_indentation` fixer

Closes GH-634.

Include spam_challenge.php only once

The file contains only definitions, and as such multiple inclusion
would never make sense.

Remove silly syntax highlighting work around

This is unlikely to be an issue nowadays.

Enhancement: Enable `single_space_after_construct` fixer

Closes GH-640.

Enhancement: Enable `indentation_type` fixer

Closes GH-622.

Enhancement: Enable `visibility_required` fixer

Closes GH-639.

Enhancement: Enable `whitespace_after_comma_in_array` fixer

Closes GH-637.

Enhancement: Trim trailing whitespace in all files

Closes GH-633.