Example queries:

Get supported ids/formats via UNAPI
libxess.php

Get supported format(s) for urn:isbn:006073132X
libxess.php?id=urn:isbn:006073132X

Retrieve urn:unsupported:xxx, should return 404
libxess.php?format=marcxml&id=urn:unsupported:xxx

Retrieve urn:bibrecord:b2275560 but request unsupported format, should return 406
libxess.php?format=an_unsupported_format&id=urn:isbn:006073132X

Retrieve urn:bibrecord:b2275560
libxess.php?format=marcxml&id=urn:bibrecord:b2275560

Retrieve urn:isbn:006073132X
libxess.php?format=marcxml&id=urn:isbn:006073132X

Retrieve urn:isbn:0585202648
libxess.php?format=marcxml&id=urn:isbn:0585202648

Retrieve Title urn:title:freakonomics
libxess.php?format=marcxml&id=urn:title:freakonomics