Implement PEP 518 and opt into PEP 517 builds

MANIFEST.in

@@ -1,3 +1,5 @@
+include pyproject.toml
+
 # Include the README
 include *.md
 

pyproject.toml

@@ -0,0 +1,5 @@
+[build-system]
+# These are the assumed default build requirements from pip:
+# https://pip.pypa.io/en/stable/reference/pip/#pep-517-and-518-support
+requires = ["setuptools>=40.8.0", "wheel"]
+build-backend = "setuptools.build_meta"

tox.ini

@@ -15,13 +15,18 @@
 [tox]
 envlist = py{27,35,36,37,38}
 
+# Define the minimal tox version required to run;
+# if the host tox is less than this the tool with create an environment and
+# provision it with a tox that satisfies it under provision_tox_env.
+# At least this version is needed for PEP 517/518 support.
+minversion = 3.3.0
+
+# Activate isolated build environment. tox will use a virtual environment
+# to build a source distribution from the source tree. For build tools and
+# arguments use the pyproject.toml file as specified in PEP-517 and PEP-518.
+isolated_build = true
+
 [testenv]
-basepython =
-    py27: python2.7
-    py35: python3.5
-    py36: python3.6
-    py37: python3.7
-    py38: python3.8
 deps =
     check-manifest
     # If your project uses README.rst, uncomment the following:
@@ -36,6 +41,7 @@ commands =
     python setup.py check -m -s
     flake8 .
     py.test tests
+
 [flake8]
 exclude = .tox,*.egg,build,data
 select = E,W,F