Add envs to test installation with different commands

[tox]

skip_missing_interpreters = True

envlist = clean, lint, py35, py36, unit, integration, stats

envlist = clean, lint, py35, py36, inst, setup, unit, integration, stats

[travis]

python =

    3.5: lint, py35, unit, integration

    3.6: py36, integration

    3.5: lint, py35, inst, setup, unit, integration

    3.6: py36, inst, setup, unit, integration

[testenv]

# install_command can be removed when --process-dependency-links is not

# needed anymore, and this section uncommented

install_command = pip install --process-dependency-links {opts} {packages}

# test that it can be installed with custom commands and clean env

[testenv:inst]

skip_install = True

commands =

    # this will fail until --process-dependency-links is not needed

    # it needs to be commented since error code will be still 1

    # - pip install .

ignore_errors = True

recreate = True

[testenv:setup]

skip_install = True

commands = python setup.py install

recreate = True

[testenv:unit]

deps = .[test]