Update Twemoji to v15.1.0

[Nerixyz]

Updates the Twemoji fork to https://github.com/jdecked/twemoji/releases/tag/v15.1.0. Notably, the family emojis have all been changed.

To update, I ran

#!/bin/sh

set -ev

cd twitter
php grab.php
php make64.php
cd ..

# Rebuild catalog.php from the original data table (full.html)
php build_catalog.php full.html >catalog.php

# Rebuild the master mapping
./download_spec_files.sh
php build_map.php

# From the final mapping, build a preview table
php build_table.php >../table.htm

# Rebuild positions and make the master spritesheets
# This step requires ImageMagick or GraphicsMagick. Versions of ImageMagick
# before 6.7 will build the images in an incorrect order, so make sure to
# update!
php build_image.php

# create quantized sheets and optimize them all
time ./quant_sheets.sh

time parallel ./optimize.sh ::: ../sheet_*.png
time parallel ./optimize.sh ::: ../sheets-*/*.png
time parallel ./optimize.sh ::: ../img-*-64/*

php find_missing.php doesn't report any missing emojis for Twitter.

[Nerixyz]

@iamcal Can I do anything further to help you get this merged?