Added a flatten() method which allows limiting the number of results.

This method is needed for the conversion of collections or arrays to single
values. Here only the first element needs to be extracted. It is more
efficient to abort the extraction process early instead of producing the full
result collection.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1512798 13f79535-47bb-0310-9956-ffa450edef68
Initial implementation of DefaultConversionHandler.

This class implements the conversion methods defined by the ConversionHandler
interface. It delegates to PropertyConverter which does the actual type
conversions. There are some protected methods which can be overridden by sub
classes in order to customize the conversion mechanism.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1512799 13f79535-47bb-0310-9956-ffa450edef68