lib: Add file name compression

Allows to compress short arbitrary strings and returns a string using base64 url encoding.

Generator for tables included and a few samples has been added. Add more to init.go

Tested with fuzzing for crash resistance and symmetry, see fuzz.go

lib/encoder/filename/fuzz.go

@@ -0,0 +1,33 @@
+//+build gofuzz
+
+package filename
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// Run like:
+// go-fuzz-build -o=fuzz-build.zip -func=Fuzz . && go-fuzz -minimize=5s -bin=fuzz-build.zip -workdir=testdata/corpus -procs=24
+
+// Fuzz test the provided input.
+func Fuzz(data []byte) int {
+	// First try to decode as is.
+	// We don't care about the result, it just shouldn't crash.
+	Decode(string(data))
+
+	// Now encode
+	enc := Encode(string(data))
+
+	// And decoded must match
+	decoded, err := Decode(enc)
+	if err != nil {
+		panic(fmt.Sprintf("error decoding %q, input %q: %v", enc, string(data), err))
+	}
+	if !bytes.Equal(data, []byte(decoded)) {
+		panic(fmt.Sprintf("decode mismatch, encoded: %q, org: %q, got: %q", enc, string(data), decoded))
+	}
+
+	// Everything is good.
+	return 1
+}