Standardize indentation.
Fix several minor issues.

Standardize several data type & element base names.
Use a custom boolean type for attributes accepting true/false.
Fix/add the include element’s src attribute.
Remove the slot attribute from helmet, chestplate, leggings & boots.
Restrict the item slot attribute to only the actual slot numbers.
Circle was spelled cirlce.
Add ‘damage resistance’ to potion types.
Merge pull request #6 from McSpider/master

Fix indentation of schema file and fix several small issues.