Add skin tone support property

Some emojis can be combined with skin tones. For example, point up: ☝ ☝🏿 ☝🏾 ☝🏽 ☝🏼 ☝🏻

Not all emojis support them though. It would be very helpful if turtle had a boolean property indicating whether the emoji supports skin tones.

See this for more information: https://emojipedia.org/emoji-modifier-sequence/