Add tox for testing

.gitignore

@@ -1,3 +1,5 @@
 __pycache__/
 *.pyc
 /dist/
+.tox
+.pytest_cache

.travis.yml

@@ -5,5 +5,5 @@ python:
   - "3.4"
   - "3.3"
   - "2.7"
-install: pip install testpath pytoml
-script: py.test
+install: pip install tox
+script: tox -e py

appveyor.yml

@@ -14,7 +14,7 @@ environment:
 install:
   - "SET PATH=%PYTHON%;%PYTHON%\\Scripts;%PATH%"
   - "python --version"
-  - "pip install pytest mock testpath pytoml"
+  - "pip install tox"
 
 build: off
 
@@ -22,4 +22,4 @@ cache:
   - '%LOCALAPPDATA%\pip\Cache'
 
 test_script:
-  - "pytest"
+  - "tox -e py"

dev-requirements.txt

@@ -0,0 +1,4 @@
+pytest
+mock
+testpath
+pytoml

tox.ini

@@ -0,0 +1,7 @@
+[tox]
+envlist = py27, py34, py35, py36, py37, pypy, pypy3
+skipsdist = true
+
+[testenv]
+deps = -rdev-requirements.txt
+commands = pytest []