Remove Python <2.7 from supported versions

[and-semakin]

Python interpreters 2.6 and below are not supported because they don't have print() function.
We can fix support for Python 2.6 adding from __future__ import print_function import, but I don't think that there is a reason to support such an old version. Older versions (2.5 and below) are completely incompatible with Python 3.

Commit that breaks Python 2.6 compatibility: a276a29

[brandon-rhodes]

The project setup.py explicitly declares support for Python 2.6, and I have not heard reports of the library failing on that Python version, nor on any earlier Python version. What exception did you see when you tried testing it?

[and-semakin]

Sorry, I created the PR without actually checking the hypothesis. I've checked all the versions until Python 2.3 and now I understand why it works.

[brandon-rhodes]

Thank you for testing it! The print(only_one_single_value) trick is very limited, but in the early Python 3 days it proved quite helpful for folks targeting 2.6, so I went ahead and used it here. I figured, for so simple a library, why not keep it compatible with every Python version for which logging existed?

[and-semakin]

Makes sense. Thanks for the library, by the way!