[FEATURE] renderText should support some run time variables

[Dhruva Sambrani]

Is your feature request related to a problem? Please describe.
Not knowing the size of the article display area prevents rendering of well flowing text, with weird break locations.

Describe the solution you'd like
Allow users to use some run time variables while calling renderText. I presume this would work like
renderText=elinks -dump -dump-width %article_width% where %article_width% be replaced with the actual value before being called.

Describe alternatives you've considered
A not so nice work around is to set the width to a very high value, which prevents weird breaks by not breaking text at all, and instead wrapping at non-word endings.