Fixes issue #164

Removed the use of flatMap() with a custom operator.
Fixing ConnectionPoolTest flakiness.
Fixes issue #164 (contd.)

Removed the use of flatMap() with a custom operator.
Use Subscriber instead of Observer
Fixes #167 #166 #164

#164: Removed flatMap() usage in HttpConnectionHandler in favor of a custom operator.
#166: Defined a facility to also specify the acceptor event loop. RxNetty defaults to an acceptor event loop with 1 thread. Also, the number of worker threads == number of available processors.
#167: Not sending Connection: keep-alive for HTTP 1.1. protocol
Merge pull request #168 from NiteshKant/master

Fixes #167 #166 #164