Allow custom colors

[eljulians]

First of all, thanks for your work! I really like k.

It would be great to have the chance to define custom colors, with environmental variables, as the predefined ones may not be suitable for every terminal color scheme

[HaleTom]

GNU ls respects $LS_COLORS.

The killer plugin to set this variable for hundreds of filetypes is: https://github.com/trapd00r/LS_COLORS

@julenpardo would #86 support this?

[V4G4X]

The way the branch name master shows up here, I was hoping if we could have an option to have it show up in a different color.
In my terminal, my background and brightness is often dark, so that the branch name isn't legible.

Similarly, is it possible to disable the rotting dates feature specifically?

For now I've had a workaround to change K_COLOR_BR to a different value like "0;33"(yellow).
But I'm sure that will cause issue whenever there's new commits.