Add border prop

[lehresman]

Is your feature request related to a problem? Please describe.

No

Describe the solution you'd like

The web version of react-fontawesome has a border prop that sets the border class. I am needing a similar feature for react-native-fontawesome. Bonus points for easily setting the border color.

Describe alternatives you've considered

I thought about layering two icons on top of each other, having the bottom one slightly bigger to be my border. But that doesn't work correctly around all curves. The scaling ratio is different. It's also kind of a hack.

Additional context

I am using faMapMarker as a pin on top of a Google map. Works great, since FontAwesome icons are just svgs. However, to make the icon look right and stand out on them map, I need to set a white border.