A bunch of new pages, split du back into osx/linux

Moved du back seperate pages for linux/osx because GNU has --max-depth, BSD has -d.

Adds:
common/: dig, gzip, rm, sort, zfs, zpool
linux/: apt-get, shutdown
osx/: airport, caffeinate, diskutil, networksetup open, pgrep, qlmanage, say, shutdown, sysctl, system_profiler

Edits:
curl: Added simple download example
du: Edited example to always show units (who wants # of blocks?)
find: Added iname and size exmaples
grep: Edited -c description
ps: Added wide lines example
ssh: edited -D description, added simple port forwarding example
unzip: added list option