Added GTest
Some changes
Some changes again
Added some tests
Updated .h file
Changed to const reference
Merge pull request #124 from k-nikolaev/lab5-stack

Lab#5 by K.Nikolaev
Updated test
Merge remote-tracking branch 'upstream/master' into lab3
Merge branch 'lab3' of https://github.com/Shiryaeva-vera/devtools-course into lab3