The intent is for every color to be stored in a rgba instance
The rgba class now stores the color in a 32 bit integer to save space
This also removes the unused class rgb and moves everything else into a
cpp file.
Many functions also had weird template parameters. For example
alpha_channel<unsigned short int> would give a 2 byte number with the
alpha channel byte in both bytes.
color_util::hex would return a hex string with alpha channel if unsigned
short int was given and without if unsigned char was given. Even more
curiously those parameters were passed to *_channel and the result
nevertheless truncated to 8bits.
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