Added advantages for using code and storyboards.
Added link to gitignore.io
Fixed typo.
Add introductory text to Common Libraries section (resolves #9)
Cover external-to-native code migration in Common Libraries section
Fix typo
Cross-link to Windows Client Good Practices
Pruned and condensed the mostly valid new points.
Merge pull request #7 from dasdom/master.

Added advantages for using code and storyboards.
With modifications.