Fix Markdown link markup
Merge pull request #704 from r-gaia-cs/fix-link-extra

Fix Markdown link markup
Avoid mention branch for novices

Close #640.

This commit uses @wking's rephrasing suggested at
https://github.com/swcarpentry/bc/issues/640#issuecomment-51368705.
Merge pull request #705 from r-gaia-cs/avoid-branch-at-novice

Avoid mention branch for novices
Merge commit 'b8b493' into adding-info-on-aliases
Modified second challange for aliases