indent_guide_options - add color option with special values

[9b528120]

Problem description

when scrolling up and down, it'd be easier to tell the level of indentation across blocks if the guide line was color coded.

Preferred solution

Add new property indent_guide_color_options

Can take the following values:

• <color code>: all guides are rendered with this color
• rainbow: the deepest indentation is found, then that many color stops are applied to the rainbow (ROYGBVioletPink) to determine the color. In this case, red is always first, pink is always last, etc.
• random: hard code a random color for each level of indentation. Hard-coded for consistency across files/machines.
• [list of color codes]: use indentation depth as index (-1), pull that color from this list. Out of bounds defaults to gray.

Alternatives

I tried to extend the built-in syntax/theme files to background-color the indentations but it was too much. Coloring the guide line is more subtle/less distracting.

Additional Information

No response