First pass at an ArchiveFileObject
Moved specific archived file fields to FileObj and just focused this object on the archive itself.
Cleaned up some of the XML and added format enumeration types.
Fixed typo in a documentation field.
Added encryption key field.
Changed Encryption_Key to Decryption_Key to better denote it's purpose and added a reference to cyboxCommon:CipherType for the Encryption_Algorithm.
Merge pull request #257 from mobhutu/issue_12

Issue 12: Archive Object