add switch op design

* fix typo

* fix typo

* fix some typos

* fix

Add `ProgramDesc` storage

* Add csp.md

* update csp.md

neural machine translation model support beam search with while op

* Add fluid_compiler.md

* Paragraphing

* update switch_kernel.md

* update the demo code

* update

Make users can access parameters of layers and their gradients.

* "remove cudnndevicecontext"

* "remove unused init code"

* "fix hash functions"

* update docs

* follow comments

* fix typo

* "change operator interface"

* "move devicepool to device_context"

* "fix operator test"

* "fix op_registry Run interface"

* "net op passed. Need to fix nccl multi-Context"

* "add nccl group function"

* "add nccl group function"

* "fix gpu count exceed 32 error"

* "fix recurrent op, nccl op"

* "change the other operators interface with Place"

* "fix typo"

* "fix pybind"

* "fix device in python side"

* "fix pybind failed"

* "add init for test"

* "fix CI"

* add design doc on keys of operator kernel type

* follow comments