Alamofire 5 support for Requests subspec

• Closed #31. Added support for Alamofire 5 in Requests subspec
• Closed #14. Added support for CDATA wrapped values (breaking change see README section)

Hotfix optional attributes

• Fixed #29. Issue with optional attributes in simple tags

Swift 5 and SPM improvements

• Merged #25. Specify response encoding in Requests subspec
• Converted to swift 5
• Improved SPM support

Swift 4.2 and tags with XML encoded values

• Fixed #23. Invalid XML string for tags with XML encoded values
• Closed #24. Fixed redundant modifier warnings
• Converted to swift 4.2

Preserve and change nodes ordering

• Closed #15. Removed stripEmptyNodes from default ReadingOptions of XMLSerialization
• Fixed #18. Added nodesOrder property in XMLMap to preserve or change the nodes ordering
• Fixed nested mapping for attributes in XMLMap

XMLStaticMappable protocol

• Added missing XMLStaticMappable protocol
• Improved required initializer in XMLMappable protocol
• Added some helpful comments

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.

Mapping Array of single object

• Fixed #5. Mapping Array of single object.
• Fixed #8. Threading problem in XMLObjectParser causing crash.

Hotfix, nodes with only attributes

• Fixed #2. Wrong XML String from nodes with attributes only.

Added innerText property in XMLMap

• Fixed changes that broke Swift 3.1 and Xcode 8.3 support
• Added innerText property in XMLMap to map directly the text of current XML node #1
• General code improvements