add check_all_images_is_used
add check highlighting code
replace png to svg
replace image to text
move unittests from clean code to refactoring lecture
convert png to svg
Merge pull request #43 from AoD314/travis

Travis
Merge pull request #44 from AoD314/01-intro-to-agile

replace several png to svg in 01-intro-to-agile
Merge pull request #45 from AoD314/02-clean-code

replace image to text
Merge pull request #46 from AoD314/03-refactoring-unittests

move unittests from clean code to refactoring lecture
Merge pull request #47 from AoD314/03-refactoring

convert png to svg