Add support for <kbd>

[lodelestra]

#129

By following the 'cite' example, this version is far better!

[willdurand]

Great! The code looks good to me. What I am wondering is how it looks in the preview?

[lodelestra]

The preview looks like this:

[lodelestra]

Whitespaces aren't allowed in a key. You can't write 'cmd + p' in a single key.
Do you want to allow whitespaces?

[willdurand]

Yep, I think spaces should be allowed. According to http://meta.stackoverflow.com/questions/270967/proper-use-of-the-kbd-tag, there is no reason not to allow them.

[lodelestra]

kbd recursive inclusion like [[ [[foo]] [[bar]] ]] isn't supported. This can be an issue too.

[willdurand]

kbd recursive inclusion like [[ [[foo]] [[bar]] ]] isn't supported. This can be an issue too.

For this, I don't think it is a bad thing to be honest.

[willdurand]

thank you for your work!