Clean location.find.surface_blocks

Don't misuse location objects, don't count air blocks, don't throw
comparison errors, ...
Add item script 'furnace_recipe', fixes #689

Allow smelting of custom items in a furnace, with some limitations.
Allow unspawned entities to identify properties

Input: <e@zombie[power=9001]>
Output: e@ZOMBIE[power=9001]
Properties are now kept when unspawned. Also now identifies from tags
when unspawned.
Add potion splash event

A quick and simple event for potions splashing
Add context.keyword to chat triggers

For use with regex based triggers.
Add element.pad_* tags

For highly specific situations in which padded / formatted text is
useful.
Merge pull request #690 from mcmonkey4eva/master

Pull request for arbitrary fixes