jni 0.18.0

Rust JNI 0.18.0

on Rust Cargo

Added

• JNIEnv#define_unnamed_class function that allows loading a class without
  specifying its name. The name is inferred from the class data. (#246)
• SetStatic<type>Field. (#248)
• TryFrom<JValue> for types inside JValue variants (#264).
• Implemented Copy for JNIEnv (#255).
• repr(transparent) attribute to JavaVM struct (#259)

Changed

• ⚠️ Switch from error-chain to thiserror, making all errors Send. Also, support all JNI errors
  in the jni_error_code_to_result function and add more information to the InvalidArgList
  error. (#242)