Catch rare weird bug with dPlayer NPC

dPlayers can construct from dNPCs - if a dPlayer NPC gets sent to a
script, fix it ASAP.
Also change the world event that this was found it not even try to send
NPCs as players.
Clean firework identification

Firework Rocket items with nothing on them should have an empty property
string, not li@0
Lighter errors in adjust

Adjust throws full exception stacktraces when there's an error... don't
do that. Just little error messages!
Fix error when clicking engaged NPCs

Trigger failed = context map not given. Just lazily generate one now.
Also, fix a typo in the drop command meta.
Fix some item handling trouble

- empty lists were considered invalid, even when intentional
- fireworks sometimes show errors
- various commands and tags don't support player/npc tags inside an item
script
Add dItem.full

Perhaps all materials with unknown datavalues should just identify the
data, so we don't need tags like this.
Also, note context.damage, which the damage trigger/action theoretically
has.
Add player can_fly mechanism

A mech to let players fly!
Also fix formatting.
Fix crafting using renamed items

i@stone[display_name=MyStone] != i@stone, which means it fails to
craft... even though it should. Only item scripts are special cases.
Fix weird error adjust NPCs

NPCs are only entities if they are spawned.
Merge pull request #775 from mcmonkey4eva/master

Pull request for item related issues and rare bugs
Merge branch 'master' of https://github.com/aufdemrand/Denizen