Support text export

[kasramp]

The idea is to empower the web browsing on older and slower devices, many of which are incapable of handling modern formats like .epub. On the browser and Wikipedia side, it would be great to allow export in *.txt along side *.html.

[kasramp]

Fix .txt export code. Example: https://kindler.ink/web/readability?url=https://stackoverflow.com/questions/46898/how-do-i-efficiently-iterate-over-each-entry-in-a-java-map&q=java+iterate+map

The exported .txt does not contain any code