v2 api for seqToseq(machine translation)

Disable test_ProtoServer on Travis CI

dataset: print download progress

fix merge conflict

add sentiment data package

I use pre-commit check all file and report is the passed.
But it is not passed in Travis, so I update __init__.py

mnist api v2

Fit_a_line v2 api

Add testing cost.

add batch reader into reader design doc

Training the understand sentiment model with the new API.

Fix k8s cluster job rerunable

semantic_role_labeling v2 api

remove osx build from CI

We don't officially support OSX.
And Travis CI takes a lot of time to build osx. (long time in pending state.
Probably because travis ci don't have enough osx machines.

Fix duplicated forward/backward in trainer.

Check system's protobuf for internal users