Add an ItemMap property

A property for map items!
Also patch some meta in ItemSpawnEgg.
Catch and warn on potential notable errors

Notable loading seems to return null sometimes. Warn rather than die.
Add matches material, script

Also remove a duplicate inventory.contains block
also comment out dead code
Ignore comments and tabs in scripts

- Comments are now permitted anywhere, even in { braced } blocks
- Tabs are now permitted, and considered to be 4 spaces
Add a generic 'block' form to PlayerStepsOn

"on player steps on block" is now valid, rather than requiring a
material.
Merge pull request #802 from mcmonkey4eva/master

Pull request for item related things