Fixed wrong example for problem f6
Merge pull request #6 from EmilianStankov/master

Fixed wrong example for problem 6 from problem set 3
Adding materials.md for week2

- Adding materials for Unit Tests and TDD
Adding uncle bob to the TDD materials
Adding problems for week2 - Unit Testing & TDD
Adding example for spacify.py
Fixed method is_timer_running()'s description
Merge pull request #7 from dtaskoff/patch-1

Rewording is_timer_running()'s description
Merge remote-tracking branch 'upstream/master'