Added support for Swift 4.2 and Xcode 10

• Added support for Swift 4.2 and Xcode 10. Fixed invalid redeclaration errors. (warnings will remain in Swift 4.1 compiler, due to the fact that IUO do not behave the same way as in Swift 4.2 compiler)
• Fixed flatMap deprecation warnings.
• Fixed support for Swift 3.0 and Xcode 8.3.
• Fixed XMLSerialization to support XMLs with XML declaration
• Improved XMLMapper to support mapping of dictionary of XMLMappable and dictionary of arrays of XMLMappable objects.
• XMLSerialization can now return array of dictionaries
• Added support to map enums with rawValue of LosslessStringConvertible.
• Added support to map array of Any with single element.
• Added tests that cover more than half of the project.