lua: Init with config and pool (#321)

* lua: Intial impl with config and pool

Signed-off-by: James Hillyerd <james@hillyerd.com>

pkg/extension/luahost/lua_test.go

@@ -0,0 +1,18 @@
+package luahost_test
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/inbucket/inbucket/pkg/extension"
+	"github.com/inbucket/inbucket/pkg/extension/luahost"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEmptyScript(t *testing.T) {
+	script := ""
+	extHost := extension.NewHost()
+
+	_, err := luahost.NewFromReader(extHost, strings.NewReader(script), "test.lua")
+	require.NoError(t, err)
+}