Fix cursor position when weapon FOV does not match player FOV

[dhkatz]

This is a PR which fixes #35

As far as I can tell this hasn't broken anything else but if someone can confirm that would be great.

I ended up adding a new function specifically for weapons because we only want to do FOV corrects for view models.

I did not automatically convert the position and angles using ENTITY:LocalToWorld(pos) because I assumed most people will be positioning view model UI relative to bone positions and ENTITY:GetBonePosition(n) always returns values in world space coordinates.

Before Fix:

gmod_huaxYFYBfd.mp4

Notice how the mouse does not line up with the cursor while the screen clicker is active (the virtual cursor is being rendered by the weapon's SWEP:PostDrawViewMode)

After Fix:

gmod_hKxs9xbz2R.mp4

I can interact with both the button positioned in the world and the button positioned on the view model accurately to the mouse cursor.

[dhkatz]

Ok it looks like this did break some things, so I might need to add a specific function for weapons like entities have

[dhkatz]

Ok I seem to have fixed the issues by adding a new function to only correct FOV using view model when rendering for a weapon

[wyozi]

Looks good, thanks. If you can just add ScrW and ScrH to .luacheckrc, I can merge this. Could also add a short mention to README

[wyozi]

Good stuff