Adds a short section to make clear that microkernel applications
can utilize fibers, and can even use them with a few microkernel
object types. Revises some link names to account for the fact that
there are now 2 sections describing fiber services.
Change-Id: I5960aea8b3959bb4a383f919882419effff5917d
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>