ck_cohort_rw: Initial implementation with validation test.

I still need to implement benchmark tests and write documentation.  The reader-writer cohort locks also required that I add a method to the existing ck_cohort framework to determine whether or not a cohort lock is currently in a locked state.
ck_cohort_rw: Cleaned up regression files from last commit
ck_cohort_rw: Added latency and throughput benchmark regression tests
ck_cohort: Fixed regression tests based on ck_cohort_rw changes
ck_cohort: Updated documentation to reflect ck_cohort_rw changes
ck_cohort_rw: Reduced line wrapping
ck_cohort_rw: Removed unused member variable
ck_rw_cohort: renamed ck_rw_cohort namespace
ck_rw_cohort: Removed backwards jump
ck_ring: Remove stale comment.
regressions/ck_ring: Allow for buffers of size 4 or more.
doc: Add ck_ring manual pages.
ck_rw_cohort: Added read-preference logic and updated validation test to use it
ck_rw_cohort: Added neutral reader-writer lock
ck_rw_cohort: Added benchmark tests for reader-writer cohort locks
merged from upstream repo
doc/ck_ring: Add ck_ring_{capacity,size} manual pages.
build: Bump version for next release.
ck_rwcohort: Renamed ck_rwcohort namespace
Merge branch 'master' of https://github.com/davidjoseph/ck