Function parse 

pub fn parse(srcset: &str) -> Vec<ImageCandidate>

Parses an srcset string and returns a vector of ImageCandidates.

Examples

let srcset = "image1.png 1x, image2.png 2x, image3.png 100w";
let candidates = srcset_parse::parse(srcset);
assert_eq!(candidates.len(), 3);
assert_eq!(candidates[0].density, Some(1.0));
assert_eq!(candidates[1].density, Some(2.0));
assert_eq!(candidates[2].width, Some(100.0));