Several updates:

Several updates:
- Consistently refer to rmlocks as "read-mostly locks".
- Relate rmlocks to rwlocks rather than sx locks since they are closer to
  rwlocks.
- Add a separate paragraph on sleepable read-mostly locks contrasting them
  with "normal" read-mostly locks.
- The flag passed to rm_init_flags() to enable recursion for readers is
  RM_RECURSE, not LO_RECURSABLE.
- Fix the description for RM_RECURSE (it allows readers to recurse, not
  writers).
- Explicitly note that rm_try_rlock() honors RM_RECURSE.
- Fix some minor grammar nits.