HTTP parsing implemented with HttpHelpers.

Original HTTP parsing types now implemented by HttpHelpers (https://github.com/gsscoder/httphelpers). No reference, it's a NuGet source package. When the project switch to .NET 4.5, it already contains an async implementation.
In this way HTTP parsing will be maintained in a separated project (that can be ever updated via source) offloading Flux from caring about HTTP implementation details.