Added redact attribute.
Simplify redact attribute (don't include regex).
Move default namespace, extra types, and root element name to IOptions interface.
Renamed IOptions to IXmlSerializerOptions.
Moved OptionsExtensions to its own file.
Moved namespaces and alwaysEmitTypes to ISerializeOptions.
Missed adding ISerializeOptions.cs to index.
Reordered parameters of XmlAttributeSerializer constructor.
A redact attribute can redact strings, enums, bools, and objects.
Slight changes to redact attribute; improved tests for it.
Implemented redacting for xml attribute properties marked with redact.
Fleshed out tests for redacting XmlAttributes.
Implemented redacting for xml text properties marked with redact.
Implemented redacting for xml element properties marked with redact.