Fixes sweble-wikitext#22: Replace old AstComparer by the new and better DeepAstComparer
Fixed AST node setters which must not return the old value any more
Fixed Span.toString() which printed wrong location when from and to were individual but equal objects
AstLocation now encodes and decodes the file name to prevent clashes with the seperating colon characters
Fixed code formatting
Fixed AstNodeImpl.clone() and AstNodeListImpl.clone() and added some documentation
Renamed TestAstBuilder.List -> TestAstBuilder.NodeList
Fixes sweble-wikitext#22 and sweble-wikitext#23

Issue #23: Make DeepAstComparer extensible to be able to compare custom types in properties or attributes
Issue #22: Replace old AstComparer by the new and better DeepAstComparer

The basic DeepComparer was extracted from project parser-toolkit and moved to project utils
Rewrote ptk-xml-tools sub-project

- XML serialization is done using xstream
- Custom serialization of data structures can now be done by extending xstream with custom converters
- Common serialization code that could also be used by e.g. json serialization was moved to ptk-common