change function to generator
sync_all and sync_exist to generator
update urllib, proxy/npm.js use generator

but SyncModuleWorker still use callback type npm.js,
so just use co wrap to thunk.
after refactor SyncModuleWorker, remove this co wrap.
change npm.js to generator
add make test-dev, fixed #259
refactor sync_module_worker
refactor sync_module_worker
fix makefile, remove eventproxy
fix return versions
fix yield gather, sync missing deps even no missing versions
Merge pull request #253 from cnpm/issue237-sync-worker

Issue237 sync worker