kernel-doc: html mode struct highlights

kernel-doc: html mode struct highlights

Johannes Berg reported that struct names are not highlighted
(bold, italic, etc.) in html kernel-doc output.  (Also not in
text-mode output, but I don't see that changing.)

This patch adds the following:
- highlight struct names in html output mode
- highlight environment var. names in html output mode
- indent struct fields in the original struct layout

Signed-off-by: Randy Dunlap <[email protected]>
Cc: Johannes Berg <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>