Update changelog for 2.0b0

CHANGELOG.rst

 Changelog
 =========
 
-`2.0a2`_
---------
+All notable changes to this project will be documented in this file.
 
-New features
-~~~~~~~~~~~~
+The format is based on `Keep a Changelog`_,
+and this project adheres to `Semantic Versioning`_.
 
-* Import Untis data from MySQL
+`2.0b0`_ - 2021-05-21
+---------------------
+
+Added
+~~~~~
+* Import data related to school terms and validity ranges.
+* Provide different Celery tasks for multiple import scenarios.
+
+Changed
+~~~~~~~
+* Rename permission rules to differentiate from internal permissions.
+
+Fixed
+~~~~~
+* Cleanly delete old break supervisions instead of just replacing them.
+* Do not import lessons without lesson periods.
+* Delete (supervision) substitutions which are out of their validity range.
+* Only import supervisions for the linked UNTIS term and not for all terms.
+* Import supervisions linked to a validity range.
+* Import absences with correct absence types and not None values.
+* Set teachers to an empty list if there are no original and no substitution teachers.
+* Call update_or_create without prefetched or joined data.
+
+Removed
+~~~~~~~
+* Remove support for XML import due to a lack of maintenance.
+
+`2.0a2`_ - 2020-05-04
+---------------------
+
+Added
+~~~~~
+
+* Import UNTIS data from MySQL
  * Import absence reasons
  * Import absences
  * Import breaks
@@ -22,35 +54,30 @@ New features
  * Import teachers
  * Import time periods
 
-Bugfixes
-~~~~~~~~
-
-* None
 
-Minor changes
-~~~~~~~~~~~~~
+`1.0a1`_ - 2019-09-17
+---------------------
 
-* None
-
-`1.0a1`_
---------
-
-New features
-~~~~~~~~~~~~
+Added
+~~~~~
 
 * Allow updating subjects, rooms and time periods from new import
 * Allow importing a new version of a timetable
 
-Bugfixes
-~~~~~~~~
+Changed
+~~~~~~~
+
+* Use bootstrap buttons everywhere
+
+Fixed
+~~~~~
 
 * Work around bug in Untis that wrongly splits classes if they contain
   spaces
 
-Minor changes
-~~~~~~~~~~~~~
-
-* Use bootstrap buttons everywhere
+.. _Keep a Changelog: https://keepachangelog.com/en/1.0.0/
+.. _Semantic Versioning: https://semver.org/spec/v2.0.0.html
 
-_`1.0a1`: https://edugit.org/Teckids/AlekSIS/AlekSIS-App-Untis/-/tags/1.0a1
-_`2.0a2`: https://edugit.org/Teckids/AlekSIS/AlekSIS-App-Untis/-/tags/2.0a2
\ No newline at end of file
+.. _1.0a1: https://edugit.org/Teckids/AlekSIS/AlekSIS-App-Untis/-/tags/1.0a1
+.. _2.0a2: https://edugit.org/Teckids/AlekSIS/AlekSIS-App-Untis/-/tags/2.0a2
+.. _2.0b0: https://edugit.org/Teckids/AlekSIS/AlekSIS-App-Untis/-/tags/2.0b0