Add class definition

[birdage]

@ocefpaf what do you think about adding a class definition to the markers. ive put an example of the proposed changes below for just the circle. Wed have to figure where to put the css, maybe folium/templates/user_defined.css? i can squash the multiple changes if we want to go down this path.

i.e we have a circle marker but we want to leverage css styling a bit more, this would aid in the following issue #524

leaflet js example

    L.circle([51.509, -0.11], 1500, {
        className:" sample-circle",
        color: 'red',
        fillColor: '#f03',
        fillOpacity: 0.5
    }).addTo(mymap).bindPopup("I am a circle.");

css style

.sample-circle:hover{
    stroke: blue;
}

normal circle

on hover

[ocefpaf]

This looks nice. I am unfamiliar with the leaflet counter part to review this right now but I will take a look at it ASAP. Meanwhile we should add a notebook example and tests.

I am not sure about providing the css. Maybe the end user should ensure that the CSS is loaded in their application. I do not think we should try to cover all the possibilities... But I am open to suggestions. What to you think @BibMartin?

[birdage]

@ocefpaf i just think we could add an empty css file that the user could add their css too 😄

[ocefpaf]

@birdage I took leaflet's approach and added the default options. See #683