tools: Add script to generate a ChangeLog file.

We don't have an explicit ChangeLog file, but don't really need one
because we use a good version control system.  This script is useful if
you need a pretty-printed ChangeLog for some reason.

tools/gen-changelog.sh

@@ -0,0 +1,12 @@
+#!/bin/sh
+
+echo "Micro Python change log"
+
+for t in $(git tag | grep -v v1.0-rc1 | sort -r); do
+    echo ''
+    echo '========'
+    echo ''
+    git show -s --format=%cD `git rev-list $t --max-count=1`
+    echo ''
+    git tag -l $t -n99
+done