Correction of (most) external URLs (issue #124)

[ichsteffen]

Replace http links with https links Replace moved links (301) with target link

Unfortunately, some external references can only be reached via HTTP.

• http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod
• http://fmc-modeling.org/
• http://www.vincehuston.org/ood/oo_design_heuristics.html

What do we do with it? (Can/should we mark this somehow in the code?)

Furthermore, some sources are no longer accessible/available at all.

• http://www.cs.umd.edu/class/spring2003/cmsc838p/Design/criteria.pdf
• http://codebetter.com/markneedham/2010/03/18/essential-and-accidental-complexity/

Fix within a new issue?

All other links return the HTTP response code 200 or 301 when queried.