ThreeMF 0.3.0

Additions

• Added Model.customAttributes for preserving non-standard attributes on the <model> element, matching Item.customAttributes
• Added Model.xmlDocument(), so a model can be serialized to XML on its own

Improvements

• Packages are now written deterministically: building the same package twice always produces the same entries in the same order with identical content
• addFile(at:contentType:relationshipType:relativeToRootModel:data:) no longer throws
• The public API is now fully documented with doc comments

Fixes

• Fixed PackageWriter producing invalid packages when a file was replaced at a path that was already added: relationship IDs could collide, and replacing a part could leave a duplicate content type override or relationship behind
• Fixed writing a model's raw XML directly via addFile (before anything serialized it) leaving the package with no content type or relationship for it, making it unreadable
• Fixed a part named with a leading slash and one without being treated as two different parts, which could produce duplicate content type overrides and relationships; addTexture and addThumbnail now return absolute part URLs as a result