Use flatbuffers for some messages from Redis. (#341)

* Compile the Ray redis module with C++.

* Redo parsing of object table notifications with flatbuffers.

* Update redis module python tests.

* Redo parsing of task table notifications with flatbuffers.

* Fix linting.

* Redo parsing of db client notifications with flatbuffers.

* Redo publishing of local scheduler heartbeats with flatbuffers.

* Fix linting.

* Remove usage of fixed-width formatting of scheduling state in channel name.

* Reply with flatbuffer object to task table queries, also simplify redis string to flatbuffer string conversion.

* Fix linting and tests.

* fix

* cleanup

* simplify logic in ReplyWithTask

doc/source/install-on-macosx.md

@@ -11,7 +11,7 @@ To install Ray, first install the following dependencies. We recommend using
 brew update
 brew install cmake automake autoconf libtool boost wget
 
-pip install numpy cloudpickle funcsigs colorama psutil redis --ignore-installed six
+pip install numpy cloudpickle funcsigs colorama psutil redis flatbuffers --ignore-installed six
 ```
 
 If you are using Anaconda, you may also need to run the following.

doc/source/install-on-ubuntu.md

@@ -12,7 +12,7 @@ To install Ray, first install the following dependencies. We recommend using
 sudo apt-get update
 sudo apt-get install -y cmake build-essential autoconf curl libtool libboost-all-dev unzip python-dev python-pip  # If you're using Anaconda, then python-dev and python-pip are unnecessary.
 
-pip install numpy cloudpickle funcsigs colorama psutil redis
+pip install numpy cloudpickle funcsigs colorama psutil redis flatbuffers
 ```
 
 If you are using Anaconda, you may also need to run the following.