"add mq2007 to dataset init"

modify seq2seq demo to show gradient/error clipping.

fix hardcoded cmake for cclient/test

move recordio to Paddle from github.com/wangkuiyi/recordio

enrich paddle built-in learning to rank dataset with the mq2007 dataset

Enable the setting of global gradient clipping threshold

correct a typo

optimize code

fix a bug

add go 1.8.1 into dev image

Add Sqrt and Reciprocal activation

Fix 2078

Implement Pserver RPC, gradient update logic, cgo part