Support pretty printing

[cardil]

Now there is no way that theme can support indenting, as it is necessary to hold indent level and to change it according to theme rules.

There should be some way that theme can change current indent level, and effectively supports pretty print.

[cardil]

Implementation proposal:

There should be added a Indentation interface that will be contained in InspectionContext. This Indentation interface should be passed to all theme methods as a parameter.

interface Indentation {
  int current();
  void increment();
  void decrement();
}

[cardil]

Cloded by merging #16