Add 4 new functions to Post().

I've added the ExpandTags() to export tags in a different way. This way
allows you to see what kind of tag the tag is. Advanced clients should
use normal Tags() and color to match what is reflected on the site.

The other 3 commands are pretty simple. Just Width(), Height(), and
Dimensions(). Dimensions just calls Width() and Height() and adds a x
in between them.