Allow generic option vars pass through to Net::Server

[miyagawa]

I'd like to keep the root option namespace to specific for plackup common variables, but it would make sense to allow some prefixed options passed through to Net::Server, such as:

starman --net_server-lock_file=/tmp/file.lock ...

or some sort.

[ap]

Maybe just --ns- as prefix? Or --nsrv- maybe? Not sure what would be good… but --net_server- is awfully long.

[miyagawa]

I'd think that they're meant to be scripted in your launcher script (init.d etc) and not for the regular command line use.

[miyagawa]

in other words, if they're commonly used, we should just give a shortcut like the current ones (keepalive, etc.)

[ap]

This was implemented by #111, which has been merged and shipped, so the issue can be closed.