Merge pull request #10 from svaksha/master

Added notes on Package Managers - explained PPA, and diff when compiling from source.
fix style
Merge pull request #11 from tndoan/master

fix style
Chapter 7 on functions FD
Credit added for Svaksha. Thank you so much!
Merge branch 'master' of github.com:chrisvoncsefalvay/learn-julia-the-hard-way

* 'master' of github.com:chrisvoncsefalvay/learn-julia-the-hard-way:
  fix style
Ch 13 - Writing good Julia half done
[minor] Fixed commands formatting and minor changes.
minor typo fixes.
renamed to CONTRIBUTORS.md as it had markdown style, changed credit link to bio page