Add xml support

[Methrat0n]

Xml is easily supported in scala since it's build in the language. This format should be an simple one to write.

This issue's PR should include three new separated projects :

• restruct-xml-reader
• restruct-xml-writer
• restruct-xml

The first project should contains the complete algebra implementation allowing to read Scala instance from XML.
The second should contains the equivalent but to write a Scala instance to XML.
The last should be a combination of the last two and allow for read / write behavior.

Each project should contains complete Unit Tests for the newly build formats.