v0.3.0 ld-signature

• fix: Make sure the correct document loaders are used.
• fix: verificationMethod should be a URI.
• feat: Optional support for Google Tink.
• feat: Reduced dependency on javax.json.
• chore: Bump nimbus-jose-jwt to 9.0.1.
• feat: Continued work on better JSON-LD support.
• feat: Updates to work with new jsonld-common-java library.
• feat: Support for Titanium JSON-LD library.
• feat: Support multiple proof objects.
• feat: Start using "proof" instead of "signature".