With this MR, the following changes are introduced:
- if a file isn't valid or its schema cannot be found, the warning message now contains the file name as shown in the TextGrid navigator in addition to its TextGrid URI. This simplifies finding the file in focus. (See screenshot which contains both an old and the new logging message.)
- a CHANGELOG has been added
- some return types have been added to improve code quality
Closes #20 (closed)
