Merge pull request #12 from cubejs/cluster3

Cluster3
Wrapped the sockets into one socket
Modifed to use cacheSocket in cache
Modifed to use cacheSocket in cache
Used axon to implement cache
Merge pull request #13 from cubejs/cluster3

Cluster3
axon rewrite
Merge branch 'cubejs-cluster3' into cluster3_axon

Conflicts:
	lib/cache.js
Rewrited cache mechanism using axon
Merge pull request #15 from cubejs/cluster3

Cluster3
~ avoid duplicate #whenStop calls
~ separate spontaneous 'disconnect' & preemptive 'dismiss' (it caused master to receive 'cluster' native 'disconnect' event)
~ worker#beforeStop to stop server not app
~ 'close' is triggered by worker#disconnect from cluster, no need to double the effort
Merge pull request #16 from inexplicable/cluster3

Cluster3
Merge pull request #17 from zhuchenwang/cubejs-cluster3

Cubejs cluster3
Merge pull request #73 from zhuchenwang/cluster3_axon

Rewrited cache mechanism using axon