Update CMakeLists.txt

This commit includes checking whether ../data directory (from build directory) and ../../stk-assets directory (from build directory) exists or not. If they don't exist, then it gives error message for the corresponding directory. I have included the code for this on line 320.
Update CMakeLists.txt
added achievement banana lover
added an achievement banana lover
merged code with upstream master
Now IA don't fire a cake if the kart is driving too slow. Also correct some comments.
Merge remote-tracking branch 'remotes/upstrem/master' into skiddingAI
Don't fire a cake if the target kart is driving too slow.
Fixing #1263 and little bit refactoring
re-adding -help
misc little changes
Merge remote-tracking branch 'remotes/upstrem/master' into skiddingAI
Use half res FBO for SSAO

SSAO is a medium frequency effect, using half res fbo is fine and
improve performance and look by doing an additionnal bilinear filtering.
Also tune up some values.
Bloom: Use power of two quads.
Bloom: Tweak the threshold.
Bloom: Weight the different sized contribution.
Apply MLAA after color_in.
Fix too dark screen with MLAA enabled.
Add an option for Tex compression

Also turn m_ssao into bool.
Add some more graphic config options.