Add gender icons

[justincy]

By gender icons we mean a generic male/female person icon that most genealogy websites use.

[justincy]

I'm not sure if I want to do this.

• Users of this library should be able to specify their own icons
• I don't want to bundle icons into this library

Given that, I see two options:

1. Share an example of how to include them yourself using purely CSS.
2. Add an optional configuration option to specify what the male and female icons are.

[justincy]

I prefer option (1).