NewLogSet returns a set of Loggers for commonly used output streams: errors,
diagnostics, stdout. The error and stdout streams should generally never be
suppressed. diagnostic can be suppressed by setting the output to
ioutil.Discard. If an output destination is not needed, one can simply
discard it by assigning it to '_'.
SetFlags is a wrapper around log.SetFlags that adds and removes, ": " to and
from a prefix. This is needed because ": " is only added by golang's log
package if either of the Lshortfile or Llongfile flags are set.