Fix GitHub links syntax in lecture 02
Swap the definitions of a global var and a constant
Merge pull request #69 from ymihaylov/fix-swap-gloabal-vars-consts

Swap the definitions of a global var and a constant
Merge pull request #70 from EmilianStankov/fix-links

Fix GitHub links syntax in lecture 02
Add lecture 03
Fix typo in example in lecture 03