* add doc for memory_optimize, test=develop

* update doc, test=develop

* doc update, test=develop

* add parallel build script to ci test=develop
* 1. classify the test case as single card/two cards/multiple cards type
   2. run test case according to the run type

test=develop

* Speed affine_channel_op unit testing
* Add check in tensor_py
* Fix ONLY_CPU Compiling

* speedup gc and inplace softmax_with_cross_entropy_grad
test=develop

* refine models gpu mem
Merge skip vars and warning messages of mem opt
remove relu mem opt
test=develop

* follow comments
test=develop

* Support seq len equal to 0 in sequence ops

test=develop

* Add more test cases

* Fix some comments

test=develop

* Fix py3 error

test=develop

* Check some shapes only in runtime

test=develop

* Follow review comments

test=develop

* Update API spec

test=develop

* fix cmakelist detecting problems

* test=develop

* test=develop

test=develop

test=develop

* fix sampling id op bug, test=develop

* fix overflow by int32 mul test=develop

* fix reference nullptr

* fix codestyle test=develop

* modify to point in ContextProjectFunctor test=develop

* modify to point in ContextProjectFunctor test=develop

* modify . to -> test=develop

test=develop

test=develop

* fix infershape in runtime

* fix infershape in runtime
test=develop

* fix infershape in runtime

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop

test=develop