Added dst (delete surrounding tag) and cst (change surrounding tag).

Not sure if this is useful more generally, but I grabbed this from Evil Surround. 

dst and cst operate on a "tag", so that given:

<p>something{cursor}</p>

and dst deletes the tags and cst' changes the tags to a single quote, etc. This makes it easier to muck around with html without having to type out the entire tag each time, since it can be inferred in these cases.