Send unmodified http request

[buger]

Currently i parse HTTP payload with golang standard http lib, and it removes/adds some headers.

We need much more simple http client that just need to send payload to the socket, without any modifications (except filters we have).

Work in progress

[buger]

Added own efficient HTTP payload modifier library which allows working with headers and path by operating with raw []byte payload.

All HTTP modification like filters or url rewriting moved to separate module (was in http output), so now it can be applied for rest of outputs as well.