Automatically generate release information (#335)

* Pull InvenTree release information from GitHub

* Cache API results to file

- Prevents rate limiting during testing

* Add 'include' file for auto-generating release notes table

* Add entry for 0.8.x

.gitignore

@@ -6,4 +6,7 @@ env/
 *.pyd
 *.pyc
 
+# Temp files
+releases.json
+
 .vscode