Better logging when encountering bad byte sequences in input

Add text snippet to InvalidByteSequenceError error message for easier troubleshooting

Fixes #59

Thanks to @elohanlon for the fix.

Add error handlers when parsing MARCXML with Nokogiri

When using nokogiri as an XML parser (default when that gem is installed and you are parsing MARCXML), previous versions would end parsing normally without throwing an exception when they encountered ill-formed XML, potentially leading to lost updates.

This version will throw an MARC::XMLParseError when it encounters badly formed XML for (all?) versions of Nokogiri when running under MRI (standard Ruby distribution).

With JRuby, XML errors will stop parsing without throwing the above exception unless nokogiri version 1.10.2 or later is in use.