Some doxygen love.
Signal - Slot communication implementation.

- Refactored code so that windows communicate with signals connected to
  slots. As Signal implementation https://github.com/pbhogan/Signals is
  used.
- Sanitized callback names.
- Popup windows are modal - to much overhead to ensure state
  consistency.
- Windows should have unique names - support for two instances of the
  same dialog that differ by title was dropped.
- Closing windows does not destroy them - only hides. Opening searches
  for existing windows, if not found creates new instance.
Various fixes and corrections

- Introduced possible option to enable C++11 support to the premake
  script. For now it is disabled as we do not need it after all.
- Disable sorting in the Treepopup.layout - we set the order by our
  selves
- Coboboxes - GetSelection lost constness
- Listboxes - Added HasItem method and support for double click events
- ScrollWidget - Added virtual destructor
- PushButtons - ConfigUpdate lost constness
Dynamic text widget support.

- Implementation of ScrollTextbox and CEGUITextbox classes.
FrameWindow extensions.

- Frame windows will have now an modality attribute.
- Added methods to find PushButtons and Textboxes attached to a window.
Implementation of Alert Popup.
Implementation of Confirm Popup.
File picker implementation.
Forgot the implementation of Frame Window modifs.
DialogManager extensions.

- Implemented a stack to track modal windows.
- Added support for AlertPopup
- Added support for ConfirmPopup
- Added support for Textbox widget
- Added support for FileDialog
Settings for syntastic and youcompleteme vim plugins.
Cleanup in external packages.
Compilation fix.
Rewrite of treebox widget.

- Support deep group structure.
Fixed display of open/close buttons in treebox widget.
First try at tree range select.
Complete implementation of range select in tree.

- Finished the implementation of range select in the treebox CEGUI
  widget.
- Documentation and comments.
Key repeat handling was buggy. Fixed.
Project data split into multiple files.

- Save project data into separate files. The file names and directory
  structure corresponds to names of ScrollEdSet sections. Initial
  implementation - lacks insertion of "include" directives into the main
  project ini file.
Finalised implementation of project save.