changed message.h, refactor things into fitler/*
Merge branch 'master' of https://github.com/mli/parameter_server

Conflicts:
	src/main.cc
	src/system/message.h
	src/system/van.cc
	src/system/van.h
rewrite the parallel match function
rewrite the parallel function
compiled successfully
fix a bug in van.cc
fix a bug in message::minicopyfrom
fix bug in parallel_ordered_match
change size_t& into size_t* in van.cc
passed key_caching and compression as filters
reorg postoffice
move things from postoffice to dashboard
add sparse_filter.h
fix a bug in ftrl