link checking of documentation #4
Description
Implement checking the documentation for broken links. This includes:
- external links (external websites sometimes can be reorganized or go down)
- internal links. Eg now I'm merging these two pages: http://alphadoc.plantuml.com/doc/markdown/en/text-encoding and http://alphadoc.plantuml.com/doc/markdown/en/plantuml-text-encoding. But I'm not sure what other pages may be referring to one or the other, so I may leave some broken links