Add <br/> elements only for two or more newlines in static pages

[gioele]

Instead of converting every newline character into a <br/> element, a <br/> element should be generated only when two or more consecutive newlines are found in a static page.

This allows the HTML elements inside static pages to be written on multiple lines. Currently they must be written all in one line otherwise spurious <br/> will be inserted in the middle, breaking the HTML result.