Mark AutoHotkey as DPI aware, retrieve DPI on startup
Add A_ScreenDPI built-in variable
Implement Gui DPI scaling, see details:

- This behaviour can be controlled using +/-DPIScale (on by default)
- Several layout constants AutoHotkey uses are always scaled
- Control positions and sizes (xN yN wN hN and relative positioning)
  are scaled in proportion to the DPI, so that scripts written for
  a 96 DPI setting can work on other DPIs. This affects Gui,Add;
  Gui,Margin; GuiControl,Move(Draw) and +MinSize/MaxSize
- Gui,Show width and height are also scaled (*not* X or Y)
- ListView column and StatusBar part widths are also scaled
- GuiControlGet,Pos returns unscaled coordinates (that is, the DPI
  conversion is undone)
- A_GuiWidth and A_GuiHeight also return unscaled coordinates
Add DPI scaling to InputBox and Progress (*not* SplashImage)
Reduced size of (rarely used) filetype icon in AutoHotkeySC.bin.
Add DPI unscaling to A_GuiX and A_GuiY
Added support for %A_LineFile% in #Include.
Merge pull request #24 from fincs/AutoHotkey_L
Fixed `class X extends Y` to allow Y to be defined after X.
Add missing initializer for mUnresolvedClasses.

As g_script has static storage duration, it is always zero-initialized;
but init anyway for clarity/maintainability.
v1.1.11.00