Code Fragment Improvements

Added

• variable --fragment-lineheight: controls the line-height of code listings.
• variable --fragment-keywordflow: controls the color of program flow keywords in code fragments. (#10)

Changed

• Improved search box close button positioning on small screens.

Fixed

• Line indentation in code fragments was broken due to my attemts to make listings overflow-scroll instead of wrap at the end of the line. This is now fixed. (#9)

Removed

• --fragment-whitespace variable. The variable is not compatible with the fix for code indentation. It's removal means that you can no longer disable the overflow-scroll in code fragments.