0.7.3: Tons of Bugfixes and more Predefined Attributes

This release makes the whole library more safe: the number of panics when reading a file was greatly reduced, now always returning an appropriate Error instead of crashing. Many minor improvements and small API changes have also been added.

New features:

• Specify an optional maximum image byte size to automatically abort reading too large images (default limit is 1GB).
• More predefined attribute types simplify handling common meta data.
• Throws more errors instead of writing invalid exr files.