Less specific to TCP and removed trivial implementation

Hey,

I was just doing some polishing. I thought it was a bit too specific to TCP, so I tried to make the introduction more general. I also removed the part of the "Trivial Implementation" after working on it for a while, because I thought it was a bit unnecessary to have this in the spec. Also the current description contradicts the rest of spec in some details.

I also did some polish and I think it's a bit more coherent and easier to read now.

Best,
Finn