INCR with initial TTL

[alexist]

Hi,

The lua.shared semantic has evolved. The method incr now accept an optional parameter init_ttl :

syntax: newval, err, forcible? = ngx.shared.DICT:incr(key, value, init?, init_ttl?)

init_ttl allow to create the missing key with a ttl and avoid to make another call to handle expiration (incr than expire)

remaining, err = dict:incr(key, -1, limit, window)

I can submit a PR to add this new optional parameter in ngx-distributed-shm

[grrolland]

Thanks for your PR.