Fixed DTLinkButton problem with superscript text

When using custom drawing for normal and highlighted text and the text had superscript then there were several problems:
- underline of superscripted text was positioned incorrectly
- underlines of a part would always extend for the entire width, instead of just be as wide as one glyph run
Changed variables to prevent side effect

If a glyph run was strike out and underlined the previous method would get incorrect position for underline.
avoid DTLinkButton frame from becoming non-integer
... due to self-adjusting to achieve minimum hit target size specified
Increase hyperlink height to be line frame height
This is how Mobile Safari appears to do it and it also reduces the likelihood that a superscript part might stick out from under the hit highlight rectangle.
Added demo case for hyperlink containing superscript text