After a talk with tgl (thanks!) about defaults, I'm convinced this is a sensible default. For people who don't like colours (myself included), telescope will honour the `NO_COLOR' env variable. Then there is also the set enable-colors = 0 for the config file. We could go further and provide a flag like -O var=value to set some values without the need for a config file eventually.

`attr' now follows the same rule as `fg' and `bg', with the three airity variant. Attributes by themselves are a comma-separated list of keywords, each one representing a ncurses attribute.

now, instead of prefix and line style, I'm adding the trailing style too. This changed the configuration syntax too.

currently unused, will help later when adding colour support