Implement a request pipe line

[pedromanoel]

Currently, the client makes request bundles of configurable size, and it will not make more requests until all are responded.

Example:
Request Bundle (0,1,2)
Piece 0
Piece 1
Piece 2
Request Bundle (3,4,5)
Piece 3
Piece 4
Piece 5

The requests should be pipelined, for better usage of network resources.
Eample:
Request Bundle (0,1,2)
Piece 0
Request 3
Piece 1
Request 4
Piece 2
Request 5
Piece 5