Replace all invocations of logging to LOG.

[seyhuns]

By means of this, logging may be disabled easily when dicttoxml is
used as a library.

Merge conflicts based on #22 are fixed.

[haplo]

It looks like there is one extra logging line that probably was added before @mfriedenhagen created his branch:

dicttoxml/dicttoxml.py

Line 36 in 75564ce

logging.info('\nLogging session starts: %s' % (str(datetime.datetime.today())))

@seyhuns Could you update that line too?

[seyhuns]

https://docs.python.org/2/library/logging.html#logging.basicConfig

I believe that set_debug function doesn't have any use case right now. It's modifying root logger which isn't used with this changes.

[haplo]

@seyhuns I think set_debug should get the dicttoxml logger and add a new FileHandler, that should avoid overriding the root handler.