Reading SKIM_DEFAULT_OPTIONS when used as a library

[MikeCain]

Hi,
I looked a little into using skim as a library, but it didn't look as though there was a way to pick up on the system-defined options like SKIM_DEFAULT_OPTIONS and SKIM_DEFAULT_COMMAND.

Does library skim have this functionality? If not, I'm interested in the potential work involved in adding that.

Thank you very much for your work on this, by the way.

[lotabout]

Currently SKIM_DEFAULT_OPTIONS is picked up by main.rs, converted to SkimOptions and passed to skim library. I'd like to keep it this way for separation concern.

I understand that reading options from environment variable could be convenient when working with skim library. Helpers might be added for constructing SkimOptions outside library in the future.