add keyrings

[mattsb42-aws]

Starting with the AWS Encryption SDK for C, we moved from master keys/providers to keyrings as a configuration/framework primitive. We need to add corresponding keyrings to this client as well.

See #150 for a discussion on the evolution of the API as we transition to Keyrings
See #153 for a discussion on the ergonomics of Keyrings

All keyring development PRs should be made to the keyring branch.

• Create keyring trace and add to encryption and decryption materials Create keyring trace and add to encryption and decryption materials. #134
• Keyring interface Defining Keyring interface, RawAesKeyring and RawRsaKeyring. #142
• KMS keyring Defining the KMS Keyring #147
• Raw RSA keyring Defining Keyring interface, RawAesKeyring and RawRsaKeyring. #142
• Raw AES keyring Defining Keyring interface, RawAesKeyring and RawRsaKeyring. #142
• Multi keyring Define the MultiKeyring #148
• MasterKeyProvider keyring Define the MasterKeyProvider Keyring. #149
• Master Key Provider Keyring Spec: #62
• Incorporate Keyrings into AwsCrypto and deprecate MasterKeyProviders Incorporate Keyrings into AwsCrypto and deprecate MasterKeyProviders. #151
• New example code for Keyrings Additional example code for Keyrings #155
• Ensure new JUnit 5 tests for Keyrings are being run as part of Travis Making tests opt-out instead of opt-in and update TestVectorRunner #154
• Update Readme example code Update Readme for Keyrings #156
• Update Changelog with new deprecation notice and Keyring features Updating changelog for version 1.7.0 #174
• Merge to master branch Merge keyring branch into master #173
• Release to Maven