* Adds KDBX4 reader/writer interfaces
* Adds KDBX4 XML reader/write interfaces
* Implements test cases for KDBX4
* Fully compatible with KeePass2
* Corrects minor issues with Argon2 KDF
Closes#6
Attachments are now stored in a pool under Metadata instead of in entries.
The protected flag of attachments isn't supported anymore.
New metadata attributes: color, historyMaxItems and historyMaxSize.
Dropped metadata attribute: autoEnableVisualHiding.
This hopefully completes support for reading/writing kdbx <= 2.14 files.
Also fix a bug in KeePass2XmlWriter so it sets Protected="True" in the Value
tag instead of Key.