Bug#836786: JavaScript beautifier added

[Emanuel Bronshtein]

js-beautify is used as JavaScript code beautifier from commit:
https://anonscm.debian.org/git/reproducible/diffoscope.git/commit/?=002f05444cc0a238d8e617b31dabef4111b4ecd2
which fix the above examples, but there are more results that have partial results in lines, such as:

in attribute inside xml file: ./usr/lib/x86_64-linux-gnu/ImageMagick-6.9.7/config-Q16/configure.xml
https://tests.reproducible-builds.org/debian/dbd/experimental/amd64/imagemagick_6.9.7.0+dfsg-1.diffoscope.html

in html file: ./usr/share/doc/singular-dev-doc/html/include_2factory_2factoryconf_8h_source.html
in .h file: ./usr/include/x86_64-linux-gnu/singular/factory/factoryconf.h
https://tests.reproducible-builds.org/debian/rb-pkg/experimental/amd64/diffoscope-results/singular.html

for some of them a beautifier will help (a good idea anyway, even if not related to this bug), a general fix as suggested in point 2 will be better (expand with JavaScript code)