remove log.debug statemens from udpserver when not running in debug mode and use arguments for string formatting on log functions

the log.debug statements are taking up a significant part of execution time (as measured by cProfile) this patch makes it so that these statement are only loaded when debug mode is True.

Changing all places (where possible) which call logger functions in combination with string formatting to use arguments on the logger function instead of doing the string formatting in place. This is a (micro-)optimalisation when the message will not be logged
fix typo in cfg.debug name
optimalisation by removing duplicate float() conversion

for these divisions we are sure that one side of the equation is already a
floating point number.

benchmark shows this can double performance for the division:

In [20]: %timeit 123/1.2
10000000 loops, best of 3: 77.1 ns per loop

In [21]: %timeit float(123)/1.2
10000000 loops, best of 3: 189 ns per loop
remove variable assignment for variable which is only used once (micro optimalisation)
revert fields[0] is a string
Merge pull request #27 from trbs/needforspeed

various optimalisations for speed