Support for message signing with RSA keys

Added RSA message signing (#16)

* Added initial RSA signing logic

* Allowed export of RSA key

* Added check for Signing Algorithm validity

* Added tests for RSA signing

* Updated README

* Readme formatting

* README update

* Added RSA guide

* Amended warning

Added support for Asymmetric ECC_NIST keys

The format for seeding files has also changed, but the original format is currently still supported.

Filter out tags

Bug fix to correctly filter out tags when listing keys.

Added support for PutKeyPolicy

Support has been added for calling PutKeyPolicy.

• Policy will accept any non-empty string.
• BypassPolicyLockoutSafetyCheck Will accept any value, including null.
• As per AWS' docs, PolicyName must be "default".

Amended environment variable naming

In order to play better with localstack, local-kms specific environment variables are now prefixed with KMS_.

Specifically:

• KMS_ACCOUNT_ID
• KMS_REGION
• KMS_SEED_PATH
• KMS_DATA_PATH

This version remains backwards compatible, with the original naming still being accepted, but a deprecated warning is now shown. The old naming will be removed in v4.

GetKeyPolicy support added

Added test for GetKeyPolicy

Updated the README.

3.0.1

Documentation update.

v3

Added support for Encryption Contexts and Tags on CMKs.

All Error and Validation messages have also been brought more inline with AWS's. This technically is a backwards breaking change for Local KMS, thus the major version bump.

2.0.1

Updated README

v2 initial release

2.0.0

Updated README