Update python and django versions

- dropped tests for Python <3.7
- dropped tests for Django <4.2
- added tests for Python 3.11, 3.12, 3.13
- added tests for Django >=4.2

as discussed in #392

tox.ini

@@ -1,21 +1,21 @@
 [tox]
 envlist =
-    py{37,38,39}-dj{22,31,32}
-    py{38,39,310}-djmain
+    py{38,39,310,311,312}-dj{42}
+    py{310,311,312}-dj{50}
+    py{310,311,312,313}-dj{51}
+    py{310,311,312,313}-djmain
 
 [testenv]
 deps =
     coverage
     django-imperavi
-    # TinyMCE above 3 doesn't support Python 3.5 anymore.
-    # TODO: Remove version freeze when Django 2.2 LTS support is dropped, early 2022.
-    django-tinymce<3
+    django-tinymce
     pytz
     webtest
     django-webtest
-    dj22: Django>=2.2,<3.0
-    dj31: Django>=3.1,<3.2
-    dj32: Django>=3.2,<3.3
+    dj42: Django>=4.2,<4.3
+    dj50: Django>=5.0,<5.1
+    dj51: Django>=5.1,<5.2
     djmain: https://github.com/django/django/archive/main.tar.gz
 usedevelop = True
 ignore_outcome =
@@ -30,14 +30,16 @@ setenv =
 
 [gh-actions]
 python =
-    3.7: py37
     3.8: py38
     3.9: py39
     3.10: py310
+    3.11: py311
+    3.12: py312
+    3.13: py313
 
 [gh-actions:env]
 DJANGO =
-    2.2: dj22
-    3.1: dj31
-    3.2: dj32
+    4.2: dj42
+    5.0: dj50
+    5.1: dj51
     main: djmain