Fixed math with non-numeric input to produce "", not its address.
Begin converting Gui commands to object syntax, see details:

- GuiType now inherits from ObjectBase.
- Gui object lifetime is now managed like all other objects, i.e.
  script variables own it. The global Gui table is just a lookup table
  now. Destroying the object also destroys the Gui.
- Introduced GuiCreate([title, options, eventPrefix])
    (Event handling system not implemented yet)
- Introduced GuiFromHwnd(hwnd)
- Disabled Gui event label system in preparation for new event system
- Converted the following Gui commands to object syntax:
  - Gui Destroy -> gui.Destroy()
  - Gui Show -> gui.Show([options, title])
  - Gui Hide/Cancel -> gui.Hide()
  - Gui Minimize/Maximize/Restore -> gui.Minimize/Maximize/Restore()
  - Gui Font -> gui.SetFont([options, fontName])
  - Gui +/-Options... -> gui.Options("+/-Options...")
  - Gui Flash -> gui.Flash([enable])
  - Gui Margin -> gui.MarginX and gui.MarginY (properties)
  - Gui Color -> gui.BgColor and gui.CtrlColor (properties)
  - {retrieving HWND} -> gui.__Handle
  - {changing title} -> gui.Title
  The corresponding old Gui subcommands have been removed.
  Automatic Gui creation has also been disabled in the Gui command
  (in preparation for its complete removal, superseeded by GuiCreate).
- The following Gui options have been removed:
  - LastFound -> use WinWait or gui.__Handle instead
  - HwndOutputVar -> use gui.__Handle instead
  - Label -> superseeded by new event handling system
Gui: rename Text control to Label control
Remove GuiType::mName.
Store the GuiType object pointer inside HWNDs for faster retrieval.
Replace global Gui array with a linked list.
Remove Gui name system.
Begin replacing g-labels with new Gui event system
Convert most Gui events to use the new Gui event handling system
Refactor dialog owning to use a HWND instead of a Gui object
Convert GuiType::CustomCtrlWmNotify().
Gui: add OnClose() event return value: 0=close, non-0=don't close
Add parameter to GuiCreate() to control ownership of the event sink
Gui: Remove OutputVars and Gui Submit.
Gui: Implement OnDropFiles() event arguments.
Remove A_Gui* built-in variables, with some side effects:

- Menu subroutines now set EventInfo to the HWND of the Gui if
  the command was launched through the Gui's menu bar. This is
  very tentatively temporary, as the Menu commands are also pending
  an object-based redesign.
- OnMessage() callbacks require usage of GuiFromHwnd(WinExist())
  and gui.Control[hWnd] to replace the "lost" functionality. Once
  again, this is tentatively temporary as per-Gui message monitors
  are planned (which will take more appropriate parameters and will
  be more flexible/easier to use).
Revert lib_pcre.vcxproj misedit
Rename gui.__Handle back to gui.Hwnd.
Change Gui lifetime management (suggested by Lexikos). Details below:

- The global Gui list now increases the reference count of the Gui.
- The extra sink ownership parameter of GuiCreate() has been removed.
- When the Gui is automatically canceled in MsgSleep(); if there is
  only one outstanding reference to it (that is, belonging to the
  global Gui list); the Gui is destroyed.
- Script::~Script() now destroys any remaining Guis for safety reasons.
Turn GuiType::mControl into an array of control pointers.