fix pip install page 404 links

Rename fill_zeros_like_op's output

* Remove unnecessary reshape in ColwiseSum

Speed up 12s -> 10s.

* Hand write ColwiseAdd in CPU

* add design doc on keys of operator kernel type

* follow comments

Add dilation for conv_trans_op

* Rename XXDescBind --> XXDesc

* Fix Compile

* Add libprotobuf-lite.a when install.

* Fix protobuf.cmake

* Bug fix

Kernel hint design

Refine elementwiseAdd and im2col

Correct the dropout_op's computation in test

* Polishing the embedding layer and the fc layer documentation
* Addressing code review feedback

* Updating the design doc of Fluid

* Organizing the operator documentation

* Adding a proposed format for operator documentation

* Adding more details to the format

* Add design of switching kernel

* Follow comments

Add python wrapper for reduce_sum

* multi cpu design

* update

* multi cpu executor to executor

* add graph converting

* use parallel operator to execute blocks with multi threads

* use auto-transpiler

* use auto-transpiler

* update

* update graph

reopen linkchecker for checking broken links in websites

Add separable convolution