Add an argument to enable/disable table de-nesting

[DavidGinzberg]

As described in source:

...
 #Removes nested tables. for handling the sins of 1990's web pages.
 #TODO: Add an argument to enable/disable table de-nesting
 [t.extract() for t in table.findAll("table")]
 #This would grab all TRs regardless of depth without the above line removing nested tables
 for row in table.findAll('tr'):
...

The table de-nesting hack is currently default behavior. For better backwards compatibility and flexibility it may be better to make it off-by-default and add a flag to enable it.