* crypto: add support for parsing SSE-C/SSE-S3 metadata
This commit adds support for detecting and parsing
SSE-C/SSE-S3 object metadata. With the `IsEncrypted`
functions it is possible to determine whether an object
seems to be encrypted. With the `ParseMetadata` functions
it is possible to validate such metadata and extract the
SSE-C/SSE-S3 related values.
It also fixes some naming issues.
* crypto: add functions for creating SSE object metadata
This commit adds functions for creating SSE-S3 and
SSE-C metadata. It also adds a `CreateMultipartMetadata`
for creating multipart metadata.
For all functions unit tests are included.
