Fast lxml-based XML plist reader/editor/writer.

• Arrays and dictionaries are lazily loaded.
• Source data is internally maintained in an lxml document.

Parsing speed using my iTunes library:

plist (http://pyug.at/Projekte/BinaryPlistLib):                 7.473s
plistlib (http://docs.python.org/2/library/plistlib.html):      7.420s
plistop (http://github.com/dw/plistop):                         0.428s

Serializing speed using my iTunes library:

plist:          5.372s
plistlib:       5.444s
plistop:        0.253s