Drop Http.fs in favor of a more intuitive, easier to use http API

[kMutagene]

The hopac dependency of Http.fs does cause a lot of problems and currently makes the Entrez API unusable. There are multiple alternatives to use simple http requests and one of those should be used instead:

• https://github.com/ronaldschlenker/FsHttp (only dependent on FSharp.Data and FSharp.Core)
• https://www.nuget.org/packages/FSharp.Data/ which seems like the underlying api of the above