Adjusted changelog for 0.1.0 release.
Cleaned/adjusted build configs and info files.

Adjusted README to be more up-to-date. Removed walls of texts related to
Git contributions in guidelines file. Added SFGUI_ROOT to FindSFGUI
search path variables. Fixed version number in Doxygen config. Removed a
lot of (unnecessary) extra options in SFGUI's main CMake config, mostly
related to linker options.
Updated SFML submodule.
Removed accidently added -std=c++11.
Updated copyright notice, adjusted Doxygen config.
Fixed WIN32 variable in CMake config.
Adjusted Linux docs install path.