* enhance ppl for all codebases
* fix dump info
* fix md and use not None
* remove redundant codes
* safe convert empty ppl tensor
* add examples and remove useless lines
* add ppl install doc and how to test a model doc
* remove mmdet model list in ppl.md
* resolve comments
* fix typo
* add mmocr doc
* mv configs as the final column
* fix typo and align tables
* fix lint