api to retrieve the VM stats

Code to expose the vm stats to couch_stats. For now just steal the code
from Folsom (https://github.com/boundary/folsom). HTTP api to expose it
is coming in another commit.
expose vm stats to the HTTP api.

GET /_stats/vm/system : system info
GET /_stats/vm/memory : memory info
GET /_stats/vm/port : ports info
GET /_stats/vm/process : process info
GET /_stats/vm/ets : ets info
GET /_stats/vm/dets : dets info
Revert "on changes, remove the connection from the pool."

This reverts commit 8d6f71e79c8382e83e9587b0d81991ec955d34bb.
use rcouch branch orf ranch
get the number of running connections

GET /_stats/httpd/connections