Image URL

[MrRobb]

Feature: Add Image faker (it's not https://www.lorempixel.com but related to #25).

[cksac]

Thanks for the PR. As #25 's discussion, we would like to use the image provider as namespace and I am not sure is it necessary to have locale for image faker. I would suggest use something like

pub enum Picsum {
    Default,
    WithSize(u16, u16),
}

or

pub struct Picsum {
   height: u16,
   width: u16,
   blur: u8,
   is_grayscale: bool,
}

then implement Dummy<Picsum> for String without locale