Automaticly sort character set

[clankill3r]

As described in the readme it is possible to change the character set:

P5_Terminal_Graphics.sequence = " /\\X";

But the characters have to be arranged in order of brightness. Having a lookup table like this:

int[] char_index_to_brightness = {...};

Could help with writing code that could sort a given character set so they user could provide the characters to be used in any order they wan't.