doc: More documentation cleanup

* move header documentations to the right doxyen group
* remove superfluous and error-prone parameters to `@file`
* re-order the module overview
* put brief to the module description where necessary
`@addtogroup` does not include a module to another module. It's an alternative to `@defgroup` in that it merges two identically named groups instead of throwing an error (see [doxygen documentation](http://www.stack.nl/~dimitri/doxygen/manual/grouping.html)).