Properly document :raising_hand:

The emoji cheat sheet used to say that you could type in "raised_hand"
to get a woman raising her hand. However, actually doing so on GitHub
and other sites just gives you a :hand:.

To get the desired emoji, you actually need to type "raising_hand"

You can see that here:
hand: :hand:
raised_hand: :raised_hand:
raising_hand: :raising_hand:

This updates the images and HTML appropriately to reflect that change.
Merge pull request #88 from wdaher/master

Update documentation for :raising_hand