Globalstorage and Anisotropic filtering

[Zardoz89]

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Adds a Global Storage of configuration values and global s if the GPU support it.

Usage :

• Call to InitGStore() at the begin of the program. Only one time necesary!
• Use Set(key, value) to remplace or create new values in the store
• Use Get(key, &value) to read values from the store. Return True if is found. If is not found, return false and not change the value

Example :

float val = 1.0f;  // Default value if it not found
Sigma::GStore::Get("foo", &val);
Bar(val); ...

[adam4813]

Can you update this PR and I will get it pulled over?