Broken links on several episodes and unclear exercise

[SilviaBuonaiuto]

I found several broken links (error 404) on different episodes :
episode 3 wildcard , episode 5 sentinel value, episode 9 referential integrity and cascading delete, episode 10 cursor.
Moreover at the end of episode 4 (Calculating new values, http://swcarpentry.github.io/sql-novice-survey/04-calc/index.html ) the “in string” function and the substring function are not very clear, maybe an example of use for these functions can be more useful than the exercise to understand them.

[henrykironde]

Thanks you @SilviaBuonaiuto, the team will look into this, I think it has something to do with the styles, but we shall get time and investigate

[henrykironde]

Thanks @SilviaBuonaiuto, I think this has now been covered in #323