The html reporter was lately a second class citizen in Pylint,
being underdeveloped and mostly neglected. It has a couple of bugs,
but the more important reason why this is removed is that we now have
a much better json reporter, which can be used as a basis for more
prettier html Pylint outputs.
Part of #975
pylint-gui was removed, because it was deemed unfit for being included
in *pylint*. It had a couple of bugs and misfeatures, its usability was subpar
and since its development was neglected, we decided it is best to move on without it.
Part of #975
Changed the documentation in couple of places, merged sections together,
described testing procedures and added more up-to-date information
in general.
