Update Fun module (#421)

* Fun: Replace ENTINDEX with TypeConversion for consistency

* Fun: Add a class wrapping player's data

* Fun: Make TraceLine a post forward

Reason: as it is it breaks plugins hooking TraceLine because of the original game call is being superceded and other modules can't catch it. It looks like it's this way from the very start fun module has been introduced 13 years ago before. Fakemeta module comes a little later.

* Fun: Clean up code

* Fun: Toggle PlayerPreThink forward on demand

* Fun: Toggle TraceLine forward on demand

* Fun: Add HITZONE* constants for use with set/get_user_hitzone()

* Fun: Refactor a litte the player class

* Fun: Clean up a little more

* Fun: Fix typo in set_user_hitzones from previous commit