Add C book "Using C on the UNIX System"

By David A. Curry. Made available for personal use by the author.
Merge pull request #804 from chastai/add-book

Add C book "Using C on the UNIX System"
[es] Adding C book
Merge pull request #805 from esparta/master

[es] Adding C book
added pt-BR version of Official Python Tutorial
Merge pull request #806 from luzfcb/patch-1

added pt-BR version of Official Python Tutorial