* Add fluid_compiler.md

* Paragraphing

* "fix decode bug"

* "follow commnet"

* "fix error"

* "fix hook bug"

* fix based comment

* fix copyright

* fix based on comment

2. Add edit distance evaluator to evaluator.py

* add new_op_kernel_en.md

* update new_op doc

* follow comment

update doc and dist test due to API change https://github.com/PaddlePaddle/Paddle/pull/7619#pullrequestreview-89656079

* update switch_kernel.md

* update the demo code

* update

* init check in for fluid dist train doc

* gramma update

* minor tweaks

* update following comments

* add copyright hook

* add copyright hook

* refine copyright hook

* "test copyright hook"

* fix check style

* fix ci

Make users can access parameters of layers and their gradients.