Name⁠space pollution

This library avoids namespace pollution and collisions:

• Macros are prefixed with PERCEPTUALCOLOR_.
• Symbols that have external linkage are within the namespace PerceptualColor. (Exception: The Qt resource system generates functions prefixed with qInitResources_ and qCleanupResources_ that are not within the previously mentioned namespace.)
• Resources within the Qt resource system are within the folder :/PerceptualColor/.