* remove python3.4 support.
Python 3.4 has reached end-of-life.
https://www.python.org/downloads/release/python-340/
* drop maximun version of pytest
* update changelog
* add laixintao to contributors, delete py34 from tox
* added black to develop guide
* no need for pep8radius.
* changelog.
* Add pre-commit checkbox.
* Add pre-commit to dev reqs.
* Add pyproject.toml for black.
* Pre-commit config.
* Add black to travis and dev reqs.
* Install and run black in travis.
* Remove black from dev reqs.
* Lower black target version.
* Re-format with black.
"\pset pager" has three possible values: "always", "on", and "off".
pgcli previously treated all non-"off" values as "always". This change
implements the expected behavior, which is to use the pager when the
output is larger than the terminal height (See \pset pager in
https://www.postgresql.org/docs/9.2/static/app-psql.html). Pgcli adds to
this by also using the pager when the output is wider than the terminal
width.
Fixes#813