allow adding arrays to header, clean up, plus rename internal class to something more useful.
allow adding arrays to header, clean up, plus rename internal class to something more useful.

pandeysoni/sendgrid-csharp,pandeysoni/sendgrid-csharp,smurfpandey/sendgrid-csharp-net40,sumeshthomas/sendgrid-csharp,FriskyLingo/sendgrid-csharp,kenlefeb/sendgrid-csharp,smurfpandey/sendgrid-csharp-net40,brcaswell/sendgrid-csharp,sumeshthomas/sendgrid-csharp,sendgrid/sendgrid-csharp,brcaswell/sendgrid-csharp,sendgrid/sendgrid-csharp,dubrovkinmaxim/sendgrid-csharp,FriskyLingo/sendgrid-csharp,dubrovkinmaxim/sendgrid-csharp,kenlefeb/sendgrid-csharp,sendgrid/sendgrid-csharp