Add GcsStore (Google Cloud storage)

Merge pull request #53 from matthewgraf/master

Bump version to 0.5.0, add changelog for GcsStore

Update S3Store to use other TransferManager methods when possible

Migrating AmazonS3 method calls to their TransferManager equivalent, which may improve reliability of transferring large files.

S3Store can now put(file.size > 5GB)

Instantiating the S3Store will require the s3.transfer.TransferManager, instead of the s3.AmazonS3.

Recommended migration:

val transferManager: TransferManager = TransferManagerBuilder.standard()
.withS3Client(yourOldClient)
.build()

val store: Store[IO] = S3Store[IO](transferManager, blockingExecutionContext = yourOldExecutionContext)