Lecture 05
Fix small typos
Merge pull request #35 from NikolayGenov/05-fix-typos

Fix small typos
Fix typos and examples in lecture 04
Merge pull request #34 from dkeranov/04-fix-examples

Fix typos and examples in lecture 04
Fix a typo in lecture 05
Merge pull request #36 from mdimitrova/05-fix-typo

Fix а typo in lecture 05
Add 2 new slides about overloading of operators

Listed all the operators, which can be redefined. Used information from the following sources:
http://ruby.about.com/od/oo/ss/Overloading-Operators.htm
http://phrogz.net/programmingruby/language.html#table_18.4

Also corrected the outdated list of instance methods of Enumerable (lazy was missing).
Merge pull request #38 from yasen23/new-slides-05

Add 2 new slides about overloading of operators
Make two links clickable
Merge pull request #37 from EmanuelaMollova/01-fix-links

Make two links clickable