Adopt native adaptive serialization, add indent toggle

[joewiz]

With eXist-db/exist#1448, eXist 3.3.0-SNAPSHOT will add native support for XQuery 3.1 adaptive serialization. Adopting this in favor of eXide's adaptive-style pretty printing would solve #154 and would go half way toward solving #147. I don't know how to apply xqlint's syntax highlighting to query results, so I won't be able to completely solve #147, but I think the benefits of native adaptive serialization — speed and accuracy — far outweigh the immediate loss of syntax highlighting.

Also, the native adaptive output supports the indent=yes|no serialization parameter, so we should add a toggle for indentation, which would affect both adaptive and JSON serialization.

[joewiz]

Closed by #168.