Merge pull request #2020 from jalyna/fix-mobile-glitches

Fix design glitches on mobile
Clean up about page
End list of completed exercises with a period instead of a comma
Merge pull request #2025 from drueck/completed-exercises

End list of completed exercises with a period instead of a comma
Move language/problem notes into x-api guide
bump ruby version in .ruby-version.example
Merge pull request #2031 from Jberczel/bump-ruby-ver

bump ruby version in .ruby-version.example
Fixing 2 links on the homepage which have invalid html
Merge pull request #2033 from leighhalliday/master

Fixing 2 links on the homepage which have invalid html
Regenerate CSS
DRY up random key generation

Remove key generation responsibility from ActiveRecord classes
Use uuid for key generation
Merge pull request #2035 from bluerogue251/dry_up_random_key_generation

DRY up random key generation
Merge master