Exempi 2.6.4 is out

Exempi 2.6.4 is out.

Here are the changes:

• Update XMPCore to Adobe XMP SDK v2023.07
  • Security Fixes.
  • Fix Exif Date missing seconds values. XMP-Toolkit-SDK issue
• Fix some portability build issues with dlopen on BSD: MR 7 (Alyssa Ross)
• Added missing file type constants from the XMP_SDK.