Use \a for all attributes in function descriptions
to avoid QDoc errors. Do not use \param, because
it is not a valid QDoc command.

Do not use \returns as it does not exist.

Do not use \brief for functions. It is not obligatory, so
rather than add them for all functions, let's consistenly leave them out.

Fix typos, grammar and style issues, and punctuation.

Change-Id: Ib8f296f93976265bb93dbeab40c5b47156518122
Reviewed-by: hjk <hjk121@nokiamail.com>