Cleanup: align command names for a couple of commands.
Cleanup: make dependency fields private - access is via "get" and "has" methods.
Fix: correctly check Heroes class.
Minor: started work on possible embedded message (mostly to support lists).

* eg. drop: [item/amount/chance/message, etc]
Add: NOBREAK argument to EXPLOSION effect (eg. event: EXPLOSION@2/FIRE/NOBREAK).  Fixes #122.
Fix: SKULL@zombie didn't work but SKULL@ZOMBIE did, fixed case sensitivity for creature skulls.
Minor: add comment