support css file
Improved underline and strike-out drawing.

Modified to avoid anti-aliasing by rounding pixels taking the context scale into account.

related to #351
deprecated method and replaced with one with options bit mask
Added ability to draw links normal or highlighted
Added contentImageWithBounds:options: method

This can be used to get an image for normal and highlighted hyperlink buttons.
removed text frame drawing on link buttons
[BREAKING] removed custom string drawing from DTLinkButton

Warning: this breaks the previous implementation approach to set attributedString and highlightedAttributedString properties. New new method is to set two different images for normal and highlighted, see DemoTextViewController implementation.
restored previous minimum hit size in demo
implemented setting a hyperlink active color

Either specify a color in the parsing options with DTDefaultLinkHighlightColor (text or color) or specify a:active in stylesheet.
Added unit test for #342
Fixed start index being ignored for OL lists
closes #342
Added unit test for #358
Ignore !important CSS tag
fixes #358
added test case comment
Made all headers public
Related to #357
added libDTHTMLParser into DTCoreText static framework
related to #357