Got rid of most bare pointers => now mostly unique_ptr.

Got rid of most bare pointers => now mostly unique_ptr.
Fixed bugs that appeared on unit tests. Added unit tests.
These are created to improve code coverage achieved using s3-tests.
Added comments and improved formatting.
Fixed improper processing when last 0-15 bytes are decoded alone.
Fixed problem with PUT with x-amz-copy-source when source object is compressed.
Fixed problem with not decrypting data on S3 copy operation
Fixed problem with syncing when object is compressed and encrypted at the same time.
Fixed retrieving original length when compression is on.

Signed-off-by: Adam Kupczyk <akupczyk@mirantis.com>