* add 'include keyboard_features.mk' into build_keyboard.mk
keyboard_features.mk is a keyboard-local version of the functions performed by common_features.mk.
* add comment into build_keyboard.mk
* added description of keyboard_features.mk in hardware_keyboard_guidelines.md.
* rename `keyboard_features.mk` to `post_rules.mk`
Many of the settings written in the `rules.mk` file are interpreted by `common_features.mk`, which sets the necessary source files and compiler options.
Many of the settings written in the `rules.mk` file are interpreted by `common_features.mk`, which sets the necessary source files and compiler options.
The `post_rules.mk` file can interpret `features` of a keyboard-level before `common_features.mk`. For example, when your designed keyboard has the option to implement backlighting or underglow using rgblight.c, writing the following in the `post_rules.mk` makes it easier for the user to configure the `rules.mk`.