add ttdiff.sh shell script by @anthrotype (#402)

tools/scripts/diff/ttdiff.sh

@@ -0,0 +1,50 @@
+#!/bin/bash
+
+# Copyright 2018 Source Foundry Authors
+# MIT License
+
+# compare fonts with ttx
+ttdiff () {
+    if [ "$#" -lt 2 ]
+    then
+        echo "Usage: ttdiff FONT1.ttf FONT2.ttf [tables ...]"
+        return 1
+    fi
+    first="$1"
+    if [ ! -f "$first" ]; then
+        echo "File $first not found"
+        return 1
+    fi
+    second="$2"
+    if [ ! -f "$second" ]; then
+        echo "File $second not found"
+        return 1
+    fi
+    tables=""
+    for i in ${@:3}
+    do
+        if [ ! -z "$i" ]
+        then
+            table="-t "
+            if [ ${#i} -eq 3 ]; then
+                # add trailing space to pad tag to four chars
+                table+="'"$i" '"
+            else
+                table+=$i
+            fi
+            tables+="$table "
+        fi
+    done
+    cmd1="ttx -q -o - $tables \"$first\" 2>/dev/null"
+    cmd2="ttx -q -o - $tables \"$second\" 2>/dev/null"
+    echo $cmd1
+    echo $cmd2
+    # colorize output if colordiff is installed
+    if `command -v colordiff >/dev/null 2>&1`; then
+        diff -u <(eval $cmd1) <(eval $cmd2) | colordiff | less -R
+    else
+        diff -u <(eval $cmd1) <(eval $cmd2) | less -R
+    fi
+}
+
+ttdiff "$@"