* [Fix] Fix free space mis-calculation when the last 01pct slot is freed.
* [Fix] Use free small memory if possible when sm space is short of.
* [Fix] Fix the wrong result of bop smget with unique option
when the first bkeys of some btrees are duplicate.
* [Fix] Fix the incr/decr operation on binary bkey value.
* [Enhance] Reduce "no more small memory check" messages.
* [Manual] Add description about smallest/largest_silent_trim.
* [Manual] Add description about bop incr/decr with initial value.
* [Other] Reinforce and reorganize arcus-memcached unit tests.
