RecurrentGroup with mixed input sequence types

Add convolution Function

Implement master client for reading training tasks

Add documentation for installing Go when building Paddle manually

No longer need to specify target_inlinks or is_seq.

update rnn doc from v1-api to v2-api.

No longer need to use SubsequenceInput. The framework will detect.

Abstract BBox and provide general functions

Fix pserver cmake

Parameter initializer in V2 API

Use CMAKE_CURRENT_BINARY_DIR instead of CMAKE_BINARY_DIR to make it more portable (when paddle is used as subdirectory)

User can provide an initializer in ParamAttr. The initializer will be called when at parameters.create().

new parameterupdater use paddle pserver cclient of go

implement master server client, remove unnecessary dummy variable