Add a bar to the left of solutions

This enables to spot them better when they are open.
99problems: Add remarks explaining code choices
taste.md: list other sites in bulleted list
taste.md: mention Code Codex site
taste.md: fix html title

Should have been done in 1e8c2775ea4227f3e3062d122f07b27d02066fab.
learn/index.md: mention Code Codex site

Should have been done in be5cf1a7abfd3c1dc9b39d5324b2d0d52be40c58.
href="about.html" -> href="/about.html"

The "about this site" link was relative, leading to 404 when clicked from a subdir (ex: go to docs and then click about).
Merge pull request #388 from klakplok/patch-1

href="about.html" -> href="/about.html"
Add CSS rules to for planet code highlighting (GaGallium)
Adding missing close paren.
Update basics.md
Import all German translations of the tutorials
Import 2 tutorial pages translated to Japanese
Import the Korean translation of the Basic tutorial
Import some tutorial pages translated to Chinese
cheat_sheets.md: minor grammar fix
cheat_sheets.md: minor grammar fix
Add French tutorial index
Finish importing all French translations of the tutorials
Create Italian tutorial index page.