support for XML Base Specification in SAX Reader

[vadim.godunko]

Several specifications utilize concepts of XML Base Specification. Although SAX EntityResolver's API was extended to provide Base_URI it is not computed now.

XML Catalogs Specification (which should be implemented under #111) also requires support of XML Base Specification.

So, this ticket is open to:

• improve implementation of XML Base;
• provide (Matreshka specific, because there are no any other specification available) API to access to value of base URI for currently processed element.

[vadim.godunko]

In [2031]:

Initial implementation of XML Base Specification support.

Refs #125.

[vadim.godunko]

In [2032]:

Update XML Conf test driver to use base URI.

Update expected test data.

Refs #125.

[vadim.godunko]

In [2033]:

Improve test driver to report base URI passed to entity resolver.

Refs #125.

[vadim.godunko]

In [2034]:

Update expected data.

Refs #125.