Add a new option for high-definition textures.
Create the directory where resized textures will be cached.
Use smaller textures when HD textures option is disabled. Generate them if they are not already in the cache directory.
Merge remote-tracking branch 'remotes/upstrem/master' into hd-textures-option
Add subdirectories in the cache directory to organize textures of each track.
Regenerate a cached texture when the original is newer.
Merge remote-tracking branch 'remotes/upstrem/master' into hd-textures-option

Conflicts:
	data/gui/custom_video_settings.stkgui
	src/states_screens/dialogs/custom_video_settings.cpp
Remove the use of cbegin and cend. (c++11 features)
Fix #1231 - stk-code/data not found on windows (secondary report).
Use instancing to expand shadows instead of GS
Remove an extra EndQuery
Make use of gl_amd_vertex_shader_layer when available
Cast some char to unsigned char
Add basic support to display GPU markers in the profiler
Merge branch 'master' of https://github.com/supertuxkart/stk-code
Remove debug arount scoped timer.
Factorize godray visibility test in its own function.
Simplify some code and have a function that render a scene from a cam pov
Fix segfault on Linux/Mesa
For some reason, glGetString(GL_EXTENSIONS) is failing. This will need more investigation
Extend caching abilities to compressed textures. Also, improve the structure of cache directories to fit new needs.