Wording.
Less magic constants.
Tasks addition and reoredeing.
Shuffling order of rotator config fields.
File rotator now can substitute `filename` placeholder.
Explicit specifying backup filenames instead of suffix.
Tiny test refactoring.
Both datetime rotator and size based one are implemented.

Matching by date time pattern as like as backup counter. Therefore, it is needed to write actual `boost_backend` implementation of mocked methods.
It can handle rotating by total file size as like as rotating by crossing some date time point.
Several tests have been written.

Massive refactoring is needed, I guess.
Task reordering: rotating feature is implemented now.
Time provider injected into rotator.
Naming.
Compatibility with GCC 4.4.