* add fused precision support for norm
* refactor code
* refactor code
* change the granularity of hook
* fix bugs if self.model is ModuleList
* add dtype condition for post hook
* refactor code for split group
* refactor code for pre/post hook
* refactor code for split group
* remove fp32 hook for norm
* unit tests for fused precision
* add doc for fused precision
* add doc for En. version
* reformat docs
* Update mixed_precision.rst
* Update mixed_precision.po
* update mixed_precision.po
Wenwen Qu