Feature 218 thread

fixes #218
Bonus points, it adds a new --threads flag/filter 
Currently there are no tests, if you are (mostly) happy with the fix and the extra functionality then I'll add some test.

## List of changes
 
teardown :
  * added new teardown method to BaseFilter
  * stubbed with empty implementation
  * changed mlogfilter to call teardown on completion of run method

conn property
  * added conn property to logevent
  * the property is generated for lines that match 'connection accepted' from the #<number>

Changed logline filter to match logevent.thread or logevent.conn so that the accept connection line is also printed