Allow supporting multiple BeforeScript and AfterScript configs

[Zhomart]

Currently these configs just replace the previous script, example:

	r.Get("/swagger/*", httpSwagger.Handler(
		httpSwagger.BeforeScript("console.log('before 1')"),
		httpSwagger.BeforeScript("console.log('before 2')"),
		httpSwagger.URL("http://localhost:1323/swagger/doc.json"), //The url pointing to API definition
	))

	// Only 'before 2' is printed

It makes hard to add multiple configuration scripts by forcing joing strings.