Add option to change default implicit uri scheme

[lampsitter]

Fixes #23

Would this work for you @JohnDowson?

[JohnDowson]

Weird issue. When doing something like this,

let cmv = CommonMarkViewer::new("TUTORIAL.md");
        #[cfg(target_arch = "wasm32")]
                let cmv = cmv.default_implicit_uri_scheme("http://127.0.0.1:8080/rack-designer/");
                        cmv.show(ui, &mut cache, TUTORIAL);

on native I get an image, while on WASM I now get a red warning icon with hover-text of "Failed to load such and such. The image format Png is not supported."
I do have the fetch feature enabled.

[JohnDowson]

Other than that, it's exactly what I've wanted.

[JohnDowson]

Weird issue. ....

Actually, this liiks like it might have more to do with @emilk 's egui_extras, given you don't seem to have any cfg gates to disable some image loaders.

[JohnDowson]

So, the work-around is to add image = { version = "0.24", features = ["png"] } to my dependencies on wasm32 targets.

Why it works without that on native is a mystery.

[emilk]

eframe uses the png feature to load the native application icon (if any).

By design, egui_extras does not enable all the image formats in the image crate, because there is a lot of them and it adds dependencies, compilation time, and binary bloat. That's why users needs to opt-in to the image formats they want.