Moved documentation to docs, recreated a simple README.txt, fixed build

--HG--
rename : doc/README-SDL.md => README-SDL.txt
rename : doc/README-android.md => docs/README-android.md
rename : doc/README-cmake.md => docs/README-cmake.md
rename : doc/README-directfb.md => docs/README-directfb.md
rename : doc/README-dynapi.md => docs/README-dynapi.md
rename : doc/README-gesture.md => docs/README-gesture.md
rename : doc/README-hg.md => docs/README-hg.md
rename : doc/README-ios.md => docs/README-ios.md
rename : doc/README-linux.md => docs/README-linux.md
rename : doc/README-macosx.md => docs/README-macosx.md
rename : doc/README-nacl.md => docs/README-nacl.md
rename : doc/README-pandora.md => docs/README-pandora.md
rename : doc/README-platforms.md => docs/README-platforms.md
rename : doc/README-porting.md => docs/README-porting.md
rename : doc/README-psp.md => docs/README-psp.md
rename : doc/README-raspberrypi.md => docs/README-raspberrypi.md
rename : doc/README-touch.md => docs/README-touch.md
rename : doc/README-wince.md => docs/README-wince.md
rename : doc/README-windows.md => docs/README-windows.md
rename : doc/README-winrt.md => docs/README-winrt.md
rename : doc/README.md => docs/README.md
rename : doc/doxyfile => docs/doxyfile