Merge pull request #162 from mdevaev/powny-ng

I will merge this PR, but only to ease collaborative development in this branch. After patches, it should be merged to master.
rename "Tabloid" requirement to "tabloid" to avoid search requests to PyPi
tox.ini: use pip instead of easy_install
.travis.yml: travis now supports pypy3
fixed flake8 warnings
fixed coverage in tox
.travis.yml: use different envs for pylint/flake8/tests
Merge pull request #163 from nikicat/powny-ng

fixed flake8 warnings
depend on kazoo.yandex >=2.0, added link to PR
configuration refactoring: shortened schema definitions
default value for api input_limit lowered 20000 -> 5000
removed longhelp Option arg
Merge pull request #164 from nikicat/powny-ng

configuration refactoring: shortened schema definitions
Removed helpers and namespace packages