update license and notices
add initial gemspec and build file
add theme argument; only change dpi if IMAGE_DPI env is set
extension enhancements

- add method to parse text into an array of text fragments
- add method to format the first rendered line (like in CSS)
- short-circuit fill_and_stroke_bounds if fill and stroke are both transparent
- advance to next page after importing page
allow heading colors to be customized, pass options to render_node_content
fully parse style attribute on span element