Use line comparison algorithm.

This implementation fails on the following tests:
- *indent of a weirdly indented vendor prefixed CSS*: nothing much can be done, the problem rises because there is too few correct indents/deindents in this file;
- *indentation stats for tabs*: I believe the test is incorrect, there really are 8 tabs.
?

It does not make sense, we are assigning the value of `diff` casted to an number to `amount`.