Function output_path 

pub fn output_path(
    input: &Path,
    suffix: Option<&str>,
    prefix: Option<&str>,
    outdir: Option<&Path>,
) -> PathBuf

Build the output path from the input path with an optional suffix/prefix/outdir (re-exported from atfits_rs). Build an output path from input with an optional suffix/prefix/outdir.

With suffix = Some("smooth") and input img.fits, yields img.smooth.fits; prefix is prepended to the filename; outdir overrides the directory.