Fix broken links

[tfausak]

I found a few broken links with https://gist.github.com/tfausak/f0581d40cc7d308aa93940cd531ccc94:

• http://blog.fightingtanukis.com/posts/2016-05-23-documentation-hierarchy.html
• http://coldwa.st/e/blog/2016-05-04-Cabal-1-24.html
• http://lwm.github.io/posts/html/document-haskell.html
• http://www.seas.upenn.edu/~sweirich/papers/systemd-submission.pdf
• http://www.snoyman.com/blog/2016/08/haskell-org-evil-cabal
• https://dl.dropboxusercontent.com/u/40457956/haskell_sucks.pdf
• https://lwm.github.io/haskell-static/
• https://lwm.github.io/stackage-8.0.2/
• https://mmhaskell.com/blog/2017/4/10/putting-your-haskell-to-the-test
• https://mmhaskell.com/blog/2017/4/3/compile-driven-learning
• https://mmhaskell.com/blog/2017/5/15/untangling-haskells-strings
• https://mmhaskell.com/blog/2017/5/8/4-steps-to-a-better-imports-list

Some of them may be false positives. It would be nice if these were checked automatically every now and then.

[tfausak]

Fixed by 6d8252d. The only one I couldn't find was http://lwm.github.io/posts/html/document-haskell.html. I opened an issue for that: https://github.com/lwm/lwm.github.io/issues/20

[tfausak]

Fixed lwm's link in b293b99.