Move text colorising stuff into a embedded plugin about oh-my-fish

[bpinto]

I like the idea, and most themes do not have as many colors as bobthefish theme.

I see them using these default colors.

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We should also improve the color functions. We always need to do this: (omf::color)$text(omf::off) it would much easier if we could achieve the following: (omf::color $text).

[donm]

In case you're still interested, @derekstavis, that issue you referenced is wrapped up now and bobthefish has multiple color schemes.

[derekstavis]

This was done as part of oh-my-fish/plugin-technicolor