Added coveralls.io coverage service.
Added symfony's filesystem lib.
Refactored tests that hit io.
Replaced native functions with symfony filesystem (less code, more error handling).
Adder filter setup and first filter.
Added negative contains filter and tested.
Added filter for regular expressions.
Fixed naming conflict and brought back mirror command.
Added more test cases.
Minor refactorings (redundant constructor arguments etc.).
Updated information, more badges and thanks.
Merge branch 'feature/filters-for-crawler' into develop