Final updates after looking over with Matt

change %pylab to %matplotlib
removed math with lists and timing comparison
added np.mean, median, sum, max, min
added filtering
Final updates after discussing with Matt

Modified selection of precip values to reflect changes in csv
file and to use pandas dataframe

modified the conversion to fractional year to use the datetime object
to get months instead of dictionary

dates are now appended to the dataframe

plotting is done using the dataframe instead of pulling out arrays

added notes to make clear what has been added to cells

Added more comments and titles
Merge branch 'master' of github.com:abostroem/2014-09-10-LBL
committing intro presentation