Fix link to Introducing Elixir in ch01.
Change hint in Etude 3.2 to use "and" instead of "commas".

The hint doesn't work in Elixir, only in Erlang.
Fix for Etude 4.3. Parameters should be "x" and "n" instead of "x" and "x"
Merge pull request #3 from benjamintanweihao/patch-2

Fix for Etude 4.3.
Merge pull request #2 from benjamintanweihao/patch-1

Change hint in Etude 3.2 to use "and" instead of "commas".
Merge branch 'master' of https://atlas-server.oreilly.com/git/1234000001642
Changes to appendix A and introduction.
Add Benjamin Tan Wei Hao to contributor list