use the XML::LibXML DOM parser instead of SAX

Testing indicates that this is significantly faster
than the alternatives (short of writing a MARC::File::XML::XS),
including XML::SAX::ExpatXS.  Since MARC::File::XML is primarily
used to process a single record at a time, memory consumption is
not an issue; once the DOM tree for a document has been used to
create a MARC::Record object, it is discarded.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>
adjust test cases for use of XML::LibXML

Neither change affects the meaning of the test.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>
add method to let client give MARC::File::XML an XML::LibXML parser

For use by applications that maintain a shared parser
object and don't want/need MARC::File::XML to have its
own.

As a side-effect, if MARC::File::XML is initializing its
own parser, it does so only when needed.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>
remove META.yml -- let Makefile.PL deal with creating CPAN metadata

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>
prepare for MARC::File::XML 1.0

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>