Added .gitattributes file for proper line endings.
Minor documentation fixes in sf::String
[Android] Implemented `sf::Window::hasFocus()`
Fixed right click not detected on OS X with trackpads, close #716

Now that `+[NSEvent pressedMouseButtons]` can be used, part of HIDInputManager becomes obsolete and is therefore removed.
Added static_cast for sf::Uint8 (fixes #731).
Reworked the UDev inclusion

* This fixes `SFML_DEPENDENCIES` missing the UDev library for static builds (issue #728).
Fixes CMake issues with udev (#734)
Added implementation of Window::hasFocus() on iOS
Replaced Xlib by XCB implementation.

* Added FindXCB.cmake script
* Added AutoPointer wrapper for automatically free'ing pointers
* Huge commit: Ported linux implementation of sfml-window to xcb
* Xcb is now used for window creation, event loop etc
* As GLX is linked to Xlib, that part of the implementation
  still uses Xlib.
* Also, some keyboard related (such as XLookupString) stuff
  is still Xlib, as xcb does not have it (yet?).
* Replaced some enums with the xcb equivalents
Adjusted and fixed XCB patch.

* Adjusted xcb_icccm calls (for recent XCB versions).
* Fixed wrong parameter order in xcb_icccm_set_wm_protocols call.
* Fixed XCB_BUTTON_RELEASE spawning a MouseButtonPressed event.
* Moved files from obsolete Linux/ to Unix/ directory.
* Added m_useSizeHints fix.
* setTitle() converts to UTF-8 before passing to XCB -> Unicode window title
  support.
* Added XCB-util dependency.
* Replaced XSelectInput. Obtaining XCB connection when taking window handle.
* Adjusted X11 example for XCB.
* Removed AutoPointer, replaced by direct XCB and free() calls.
* Added key repeat workaround.
Source code format.
Fixed WindowImplX11::getPosition.
getPosition workaround for X11. Fixed memory leaks.