Pallet dispatchable+storage doc module. (#13341)

* doc-only pallet

* cargo fmt

* generics fix for dispatchables

* use a module instead

* add doc comment warning that the dispatchable functions are generated

* clean up

* fix typo

* hide Instance4-Instance16 from `pallet` module docs

* revamp Instance1-16 comment

* Document storage types

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* fmt

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

* remove unused variables

* crate::Call => Call

Co-authored-by: Bastian Köcher <git@kchr.de>

* fix indentation

Co-authored-by: Bastian Köcher <git@kchr.de>

* remove unneeded block

Co-authored-by: Bastian Köcher <git@kchr.de>

* don't need a Vec

Co-authored-by: Bastian Köcher <git@kchr.de>

* add "doc only" to coment

Co-authored-by: Bastian Köcher <git@kchr.de>

* crate::Call => Call

Co-authored-by: Bastian Köcher <git@kchr.de>

* cargo fmt

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Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Sam Johnson <sam@durosoft.com>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Bastian Köcher <git@kchr.de>
Co-authored-by: parity-processbot <>