use htmlcoverage

.gitignore

@@ -21,3 +21,4 @@ src/icalendar.egg-info/
 develop-eggs/
 eggs/
 parts/
+htmlcov/

tox.ini

@@ -10,4 +10,4 @@ commands =
     coverage erase
     coverage run --source=icalendar --omit=*tests* {envbindir}/unit2 discover icalendar []
     coverage report --omit=*tests*
-    coverage xml --omit=*tests* -o {toxinidir}/coverage-{envname}.xml
+    coverage html --omit=*tests*