First pass at quota-used-bytes for address books per RFC 4331.

Signed-off-by: Alex Zepeda <alex@inferiorhumanorgans.com>
Add debugging flags in the form of environment variables.

MEISHI_DEBUG_XML_REQUEST: If >=1 log the XML request.  If >=2 pretty
print it.

MEISHI_DEBUG_XML_RESPONSE: If >=1 log the XML response.  If >=2 pretty
print it.

MEISHI_DEBUG_SUPPORTED_PROPS: If >= 1, log unsupported properties from
PROPFIND requests. If >=2, also log problems parsing the supported
properties array and the list of supported properties for a class.

Signed-off-by: Alex Zepeda <alex@inferiorhumanorgans.com>
Beef up the REPORT debugging.

MEISHI_DEBUG_REPORT: If >=1, perform rudimentary logging (report name
and depth header.

MEISHI_DEBUG_REPORT_LIST: If it contains 'multiget', log extra info
about the addressbook-multiget report.

Signed-off-by: Alex Zepeda <alex@inferiorhumanorgans.com>