Addresses #1 : Autogenerate ID numbers for objects with 'id: null' in their YAML

This also changes the way scripts are serialized. Scripts are serialized with a magic number, but I couldn't figure out how it was calculated. Thankfully, the editor does not appear to care about the number - at least, VX Ace doesn't - so I just got rid of it, and used the same sequential ID numbering that is used in the rest of the YAML structures. Works great.

Items with an ID already set should be preserved, so you should be safe to do this without worrying about references to item ID numbers changing in events & etc. In other words, this should be collaboration-safe.
Addresses #1 : Prevents loading duplicate ID entries from YAML

If the yaml loader detects a duplicate ID (2 items with ID #12 for example), then the import will abort.

Also adds formatador for pretty output and easier parsing of errors.