Documentation cleaning.
- Formatting and grammar edits on recently added docs.
- Added missing NPC header and script conf include from ea8ccfc.
- Moved ER model files to a separate folder ('doc/model/').

Fixed a typo in Wolfchev instance. (bugreport:9263)
http://rathena.org/board/tracker/issue-9263-wolfchevlaboratory-script-error/

Signed-off-by: Euphy <euphy.raliel@rathena.org>