This adds several helper functions for serializing to XML:
* ol.xml.serialize: Counterpart to ol.xml.parse. By splitting
the serialization process up into a node factory and a node
writer, note writers can easily be used for different
namespaces.
* ol.xml.pushSerializeAndPop: Counterpart to
ol.xml.pushParseAndPop.
* ol.xml.makeStructureNS: Works like ol.xml.createParsersNS,
but works for arbitrary structures.
* ol.xml.makeChildAppender: If the top item of the stack has
the new ol.xml.NodeStackItem type, this helper function
can be used to create a serializer that appends the current
node to its designated parent.
* ol.xml.makeChildNodeFactory: Creates a node factory which
produces child nodes from an array of node names which are
passed to ol.xml.serialize.
* ol.xml.makeSequence: A convenience function for creating
xsd:sequence structures. Takes an object literal and an
ordered list of the keys, and returns an array that can be
passed as values to ol.xml.serialize.
* ol.xml.makeSimpleTypeWriter: Using e.g. the new write*TextNode
functions from ol.format.XSD, this function creates a node
writer that writes simple type nodes for values like strings
or numbers.
The following commits will be using this new framework for
implementing ol.format.GPX.writeFeatures, and prose
documentation with instructions based on what was said above
will be added.
