add script to automate fuzzing

.gitignore

@@ -6,3 +6,5 @@ _obj
 _test*
 markdown
 tags
+fuzz-workdir/
+markdown-fuzz.zip

s/fuzz.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+set -u -e -o pipefail
+
+# This runs a go-fuzz as described in:
+# https://medium.com/@dgryski/go-fuzz-github-com-arolek-ase-3c74d5a3150c
+# https://github.com/dvyukov/go-fuzz
+
+go get github.com/dvyukov/go-fuzz/go-fuzz
+go get github.com/dvyukov/go-fuzz/go-fuzz-build
+
+# this step is expensive, so re-use previous runs if possible
+if [ ! -f ./markdown-fuzz.zip ]; then
+    mkdir -p fuzz-workdir/corpus
+    cp testdata/*.text fuzz-workdir/corpus
+    echo "running go-fuzz-build, might take a while..."
+    go-fuzz-build github.com/gomarkdown/markdown
+fi
+
+echo "running go-fuzz"
+go-fuzz -bin=./markdown-fuzz.zip -workdir=fuzz-workdir