Merge pull request #4 from Shekeen/master

Corrections and changes
Merge pull request #5 from Shekeen/master

Translation for two more parts
Added chapter about hackage. Part 1 is now finished.
renamed:    chapters/12-hackage.md -> chapters/12-about_hackage.md
Small language fixes.
Merge pull request #6 from zudov/chapter02

Chapter02
Correct name of module from text package.
Correction of Haskell code examples.
Added "Pure Functionality" chapter
Removed comma
Merge pull request #7 from zudov/pure_functionality

Pure functionality
Merge changes from jhenahan/master