Add smudge and clean filters to automatically set edit date.

.gitattributes

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+# Date keyword expansion
+specs/latest/**/index.html filter=dater

.gitconfig

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+# Filters used by WebGL repo
+[filter "dater"]
+    smudge = bash expand_date %f
+    clean = bash -c \"sed -e 's/\\(<span id=\\\"LastEditDate\\\">\\).*\\(<\\/span>\\)/\\1\\2/'\"
+    required
+
+# Needed to avoid merge conflicts
+[merge]
+    renormalize = true

.gitconfig.sh

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+#!/usr/bin/env bash
+
+# Set colors
+GREEN='\033[1;32m'
+NC='\033[0m'
+
+# Connect repo's .gitconfig
+git config --local include.path '../.gitconfig'
+printf "${GREEN}Git config was successfully set.${NC}\n"
+

expand_date

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+#! /bin/bash
+
+# Smudge driver for the kwexpander filter for expanding keywords. Currently
+# only $Date$ is supported.
+#
+# See CONTRIBUTING.md for usage information.
+
+last_date=$(git log --pretty=format:"%ad" -1 HEAD -- "$1")
+sed -e 's/\(<span id=\"LastEditDate\">\).*\(<\/span>\)/\1'"$last_date"'\2/'
+