API: Added new API funcs

[lozatto]

No description provided.

[dystopm]

I think most of them are a great addition and will help more than one coder, BTW I got some observations:

• There are functions here that are already exported. I must remind you that the ReGame API is not the only interface that is exported here: enginefuncs_t includes SetSize, SetOrigin, PointContents and FindEntityInSphere. I don't see the point in adding them redundantly.
• UTIL_CountEntities is a miscellaneous one (did myself) and can be done in any metamod/amxx subplugin even without using regame. There's a NEED in exporting them?
• Are you aware that UTIL_IsSpawnPointOccupied is bugged and is also not being used? 👀 (it needs NOXREF tag also) (VEC_SPOT_HULL_MIN/MAX vectors are not considering negative height)

EDIT: I'm quoting @wopox1337 here:

Just use Hamsandwich, there will be no difference in performance. your requests for code convenience are strange, all your problems are completely solvable without reapi and code complications.