Open External Links in New Window

I am viewing this document with Firefox's internal pdf viewer, which results in
opening all external links in the same tab as the document itself.

See https://en.wikibooks.org/wiki/LaTeX/Hyperlinks#Customization for the option
pdfnewwindow "define if a new window should get opened when a link leads out of
the current document".

I am not sure of one should add this option to
  fonts/opensans/doc/fonts/opensans/opensans.tex
too.
Move setting to hypersetup
Merge pull request #31 from ax3l/external-links

External links