merge with lasted develop branch. Optimizer lib2

Repeat layer for column vector

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

Also remove active_type argument for many layers in config_parser.py because it is automatically
handled by LayerBase.

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().