and refactor code, inlining auxiliary functions inside
`prompt_eriner_main`.
Theme colors are now customizable with parameters. Also, it works better
with light backgrounds by using `%Sstandout%s` for the segments which
were originally using black as foreground color (intended for dark
backgrounds).
The help explains the parameters, and the preview shows one color
variation.
Fixes#169. Closes#226.
39e961117d