Added pypy to tox and travis build; improved linting.

.travis.yml

@@ -10,11 +10,18 @@ matrix:
       env: TOXENV=py37
     - python: 3.8
       env: TOXENV=py38
+    - python: pypy3
+      env: TOXENV=pypy3
     - python: 3.8
-      env: TOXENV=docs
+      env: TOXENV=lint,docs
+      install:
+        - pip install tox
+      script:
+        - tox
 
 install:
-    - pip install tox
+    - pip install tox coveralls
 
 script:
     - tox
+    - coveralls

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py37,py38,docs
+envlist = py27,py37,py38,pypy3,lint,docs
 skipsdist = True
 
 [testenv]
@@ -8,10 +8,29 @@ deps =
   py27: -r requirements/dev-py2.txt
   py37: -r requirements/dev-py3.txt
   py38: -r requirements/dev-py3.txt
+  pypy3: -r requirements/dev-py3.txt
 commands =
-  pytest -q -x --pep8 --doctest-modules \
+  pytest -q -x --doctest-modules \
     --cov-report term-missing --cov wheezy.core --ignore demos
 
+[testenv:lint]
+basepython = python3
+skip_install = True
+deps =
+  flake8
+  flake8-bugbear
+  flake8-import-order
+  flake8-mutable
+  pep8-naming
+commands =
+  flake8 demos doc src setup.py
+
 [testenv:docs]
 deps = -r requirements/docs.txt
 commands = sphinx-build -a -b html doc/ doc/_build/
+
+[flake8]
+show-source = True
+max-complexity = 10
+# Codes: https://www.flake8rules.com/
+ignore =