XQilla version 2.2.0 released

This is the 2.2 release of XQilla. This release adds a debugger and
debugging API, partial support for XSLT 2.0, and a prototype
implementation of higher order functions for XQuery.

XQilla is an XQuery, XSLT 2.0 and XPath 2.0 implementation written in
C++ and based on Xerces-C. It implements the DOM 3 XPath API, as well
as having it's own more powerful API. It conforms to both the XQuery
and XPath 2.0 W3C recommendations.

Change log:
* Added a debugging API, and a command line debugger invoked by passing
a "-d" flag to the command line tool.
* Added a partial implementation of XSLT 2.0. This should currently be
considered alpha quality.
* Added an implementation of the current draft of XQC, a standard C API
for accessing XQuery implementations.
* Added a prototype implementation of higher order functions for XQuery.
* Added the ExternalFunctionResolver API to resolve implementations for
external functions that are unknown before compile time.
* Added the xqilla:analyze-string() extension function for performing
complex regular expression analysis.
* Added query options for controlling schema validation, document
projection and lint warnings.
* Added a --disable-rpath configure option for maintainers.
* Implemented function and variable inlining, and other partial
evaluation optimizations.
* Implemented tail recursion optimization.
* Modified XQilla to compile against Xerces-C 3.0. A source installation
of Xerces-C is no longer necessary for compilation.
* Improved static typing with cardinality information.
* Fixed a bug in schema validation of a document in no namespace.
* Fixed schema validation to check ID/IDREF constraints correctly.
* Fixed a bug in validation of SequenceTypes like
document-node(schema-element(XX)).
* Fixed a bug in re-writing documents to disk after updating them, when
they have a space in their document URIs.