Implement issue #6

[k-g-a]

Implements #6

Also added .idea folder (generated by JetBrains WebStorm) to .gitignore. Unfortunatelly, many tests are failing on windows due to slashes mismatch. I've checked manually and the only non-slash failing test is "uses 0 as relative threshold if no threshold is provided": Expected mock function to have been called with: {"pixelThresholdRelative": 0} as argument 2, but it was called with {"colorThreshold": 0, "pixelThresholdRelative": 0}. But it seems unrelated to changes made in this PR.

[coveralls]

Pull Request Test Coverage Report for Build 47

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.121%

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Totals
Change from base Build 46:	0.0%
Covered Lines:	388
Relevant Lines:	388

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💛 - Coveralls