Added support for signed 64 bit integer value computation into the script engine.
This is required because newer official features require support for bigger numbers inside the scripts.
This also cleans up a lot of messy code and fixes a few issues like script stack corruptions.
Thanks to @aleos89 and everyone who supported me with this.
* Alphabetically sorted includes.
* Updated copyright and license text to match across all files.
* Removed pragma once define in header files in lieu of ifdef guards.
* Follow up to 2746e0d
* Cleaned up some variable assignments when parsing the packet.
* Updated packet documentation.
* Freed message 220.
Thanks to @RadianFord and @Lemongrass3110!
