Fixing salaxb so it can compile Footprint XML Specification.

First I had to account for the fact that in XML Schema, you could legally have elements having the same name as long as they are not at the top level. This required me to change the parsing a little bit. Next, I was fixing the simple content handling, I ran into the following error message by Scala compiler:

   [scalac] tests/tmp/footprint.scala:255: error: value Tuple23 is not a member of package scala 
   [scalac] case class VolunteerOpportunity(volunteerOpportunityID: Option[String],
   [scalac]            ^
   [scalac] one error found

This is because Scala supports only up to Tuple22.

There's a great article about XML Schema called Understanding W3C Schema Complex Types by Donald Smith. I wish I've read this earlier. The author summarizes the complex types into four simple points:

• derivation (restriction, extension, list, and union) is the basis of connection between types in the type hierarchy.
• the initial branching of the hierarchy is into simple and complex types.