Switch InventoryContents default "0" to "i@air"

This occasionally threw errors, so might as well.
Add dPlugin, some more server tags

This adds a dPlugin dObject, which is a way to get (basic) information
from external plugins.
Update meta
Merge pull request #616 from Morphan1/master

Requesting pull, sir.
Merge branch 'master' of https://github.com/aufdemrand/Denizen