I rewrote the header splitting to ignore all whitespaces after ':', it will now also directly allocate key and value from the *char.

This is a bit faster than strings.SplitN(C.GoStringN(cstringForSplit, length), ": ", 2), but only a small optimization in the context of a whole request.

Test with go test -bench=. (only splitting this specific header without adding it: "Header-Key: value")

BenchmarkHeaderSplitOld-20              21330975                50.82 ns/op
BenchmarkHeaderSplitNew-20              39266910                29.69 ns/op