New upstream version 0.9.0

.github/workflows/CI.yml

.github/workflows/release.yml

.github/workflows/snapshot.yml

.gitignore

.travis.yml

README.md

RELEASE_NOTES.md

build.sbt

...e/src/main/java/org/msgpack/core/ExtensionTypeHeader.java

msgpack-core/src/main/java/org/msgpack/core/MessagePack.java

...ck-core/src/main/java/org/msgpack/core/MessagePacker.java

...-core/src/main/java/org/msgpack/core/MessageUnpacker.java

.../main/java/org/msgpack/value/ImmutableTimestampValue.java

...-core/src/main/java/org/msgpack/value/ImmutableValue.java

...-core/src/main/java/org/msgpack/value/TimestampValue.java

msgpack-core/src/main/java/org/msgpack/value/Value.java

...ck-core/src/main/java/org/msgpack/value/ValueFactory.java

msgpack-core/src/main/java/org/msgpack/value/ValueType.java

msgpack-core/src/main/java/org/msgpack/value/Variable.java

...n/java/org/msgpack/value/impl/AbstractImmutableValue.java