* add paddle new save load doc

* move static save apis & polish multiple details

* add api mapping

* move apis place

* fix example code error

* polish model save load guide

* polish example code

* fix details example error

* polish guide doc

* change title format

* remove history reason

* remove other history reason

* add enable_static for old save/load

* add enable_static for old api

* add missing get_program_persistable_vars and get_program_parameter doc
test=develop

* add missing save doc, add link
test=develop

* update load api_cn, test=develop

* polish api comment, test=develop

* fix code bug, test=develop

* polish api comment, test=develop

test=document_fix

* add save load save_dygraph load_dygraph, test=develop

* add .idea in gitignore, test=develop

* minor fix, test=develop

* doc refines, test=develop

* doc refines, test=develop