Adds basic tests for ringo/httpserver and support for multiple headers

This pull requests adds support multiple header fields in the request, which is described in RFC 2616 - 4.2 Message Headers. Please note that commit 5e63a4ff47cb40c9c8fc71786b6d301c510422a9 does not establish full compliance to JSGI 0.3 (Level 0/A Draft 2), since the spec proposes an array. Instead we use the serialization into one single value, but it's easy to create an array by splitting the comma-separated field.