Add ofp_requestforward

Signed-off-by: Simon Horman <horms@verge.net.au>
Add ofp_requestforward encoder

Signed-off-by: Simon Horman <horms@verge.net.au>
Add ofp_requestforward decoder

Signed-off-by: Simon Horman <horms@verge.net.au>
Merge branch 'v5-requestforward' of github.com:horms/of_protocol into v5

This closes #70.

Conflicts:
	include/ofp_v5.hrl
	src/ofp_v5_decode.erl
	src/ofp_v5_encode.erl