add groupStats module
fixe line break

add missing to_string function
add interface module for groupStats
fix bits shift
fix the test, and add rountrip test for GroupStats
fix indent issue
use of max_uint32 value
rename module Table, Aggregate, Flow to TableStats, AggregateStats, TableStata
move of ofp_flow_stats cstruct
Merge pull request #3 from fugitifduck/multipartReply

Blocking issues for merge