Added ability to specify window icon (external application window) using an Image resource and SDL cross platform capability
Added Script Bindings in Lua and Angelscript to support the function
Added functionality to set the value for a node in the form of <node>value</node>.
Added method to retrieve the value of a node held in the inner xml tags eg. <node>value</node> would return "value" when called on "node"
Added Script Methods for Getting and Setting the value as detailed above (Lua contains Getter only inline with the rest of the functionality)
Removed OpenGL scratch buffer allocation log spam, even in debug mode.
Merge remote-tracking branch 'remotes/alexparlett/window-icon'
Merge remote-tracking branch 'remotes/alexparlett/xml-value'
Normalize whitespace, update documentation.
Added AngelScript & Lua property accessors for the XMLElement's value.
Added setters for Lua XMLElement.
Updated scripting documentation.
Added Image::GetSDLSurface() to avoid code duplication. Fixed crash from null image pointer in Graphics::CreateWindowIcon().
Fixed XMLElement on GCC.
Fix function order in header.
Fix Mac OS X and iOS build from external CMake project.

Since the CMake minimum is bumped up, set the policy CMP0022 to NEW. Incidentally it is also required to be so to stop the static libraries dependency from being transitively get included to other targets that links to Urho3D shared library.
Clean up scene node related comments in samples.