Fixed stack acciddent bug in PlayerOptions lua functions.  Added skew and tilt mods to PlayerOptions::GetMods and FromOneModString for when the perspective isn't one of the old ones.
Made PlayerState:GetCurrentPlayerOptions safe to use.  Added Docs/Themerdocs/modslevel.txt to explain what ModsLevel should be used by a theme using the new PlayerOptions interface.
Merge pull request #150 from kyzentun/player_options_fix

Fixed stack acciddent bug in PlayerOptions lua functions.