[PATCH] Doc/kernel-doc: add more usage info

- Add info that structs, unions, enums, and typedefs are supported.

- Add doc about "private:" and "public:" tags for struct fields.

- Fix some typos.

- Remove some trailing whitespace.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>