tox += build; legibility fixup

Based on suggestions from @stevepiercy:

- split lint into lint (doing only checks) + build - to build
  sdist/wheel to distribute:

  https://github.com/Pylons/zodburi/pull/30#discussion_r630537231

- structure list of environment for readability:

  https://github.com/Pylons/zodburi/pull/30#discussion_r630523259

tox.ini

 [tox]
 envlist =
-    lint
-    {py27,py35,py36,pypy,pypy3}-{zodb4,zodb5},{py37,py38}-zodb5,cover,docs
+    {py27,py35,py36,pypy,pypy3}-{zodb4,zodb5},
+    {py37,py38}-zodb5,
+    cover,docs,lint
 
 [testenv]
 commands =
@@ -44,11 +45,21 @@ deps =
 skip_install = true
 commands =
     check-manifest
-    # build sdist/wheel
-    python setup.py sdist
-    python setup.py bdist_wheel
-    twine check dist/*
 deps =
     check-manifest
-    readme_renderer
+
+[testenv:build]
+skip_install = true
+commands =
+    # clean up build/ and dist/ folders
+    python -c 'import shutil; shutil.rmtree("dist", ignore_errors=True)'
+    python setup.py clean --all
+    # build sdist
+    python setup.py sdist --dist-dir {toxinidir}/dist
+    # build wheel from sdist
+    pip wheel -v --no-deps --no-index --no-build-isolation --wheel-dir {toxinidir}/dist --find-links {toxinidir}/dist zodburi
+    twine check dist/*
+deps =
+    setuptools
     twine
+    wheel