v0.2.0 did-common-java

• feat: Reduced dependency on javax.json.
• feat: Add methods to express DIDs and DID URLs as JSON.
• fix: Fix loading of JSON-LD contexts.
• feat: Keep "publicKey" as a transitional feature for now.
• feat: Continued work on better JSON-LD support.
• fix: Various updates to JSON-LD handling.
• fix: Re-organize JSON-LD contexts.
• feat: Many updates to JSON-LD structure and processing.
• feat: Use latest DID ABNF for parsing.
• fix: Remove dependenies on jsonld-java.
• feat: Update JSON-LD contexts.
• feat: Support for Titanium JSON-LD library.
• fix: Update pom.xml configuration.
• feat: Add media types.
• fix: Support for latest syntax, per w3c/did-core#334