Improved metadata support via EXIF metadata. Since JXR is based on a TIFF container, EXIF data is read directly from the file so it always works (even with versions of libjxr that don't have the metadata reading API).
It also solves the following issues:
- Incorrect date format on saved JXR files (was saved in ISO format instead of `yyyy:MM:dd HH:mm:ss`).
- Incorrect date type setting in EXIF data: the `DateTime` tag should be updated on every save (verified by GIMP and Photoshop). Our `CreationDate` metadata is the equivalent of the EXIF `DateTimeOriginal` tag.
Closes#22
The goal of MR is to control the correct saving of metadata and resolution in plugins that support them.
- Modified the basic write test to verify that resolution and metadata are saved correctly.
- Verifies the correct functioning of MicroExif in plugins that use it to save metadata.
- EXR: fixed wrong vertical resolution (error found with this MR).
- Added EXR, JXR, JXL, PCX metadata test.
