Add flake8 tox env

tox.ini

@@ -8,3 +8,20 @@ commands = python lesscpy/test/__main__.py -v
 [testenv:pep8]
 deps = pep8
 commands = pep8 --repeat --show-source --ignore=E501 --exclude=.venv,.tox,dist,doc lesscpy
+
+[testenv:flake8]
+commands = flake8
+
+[flake8]
+# F811: redefinition of unused 'client' from line 81
+# F821: undefined name
+# F841: local variable is assigned to but never used
+# H201: no 'except:' at least use 'except Exception:'
+# H202: assertRaises Exception too broad
+# H302: import only modules
+# H304: no relative imports
+# H404: multi line docstring should start with a summary
+# H802: git commit title
+ignore = F811,F821,F841,H201,H202,H302,H304,H404,H802
+show-source = True
+exclude = .venv,.tox,dist,doc,*egg,build