Updated Avro schema to support null values for fields that do not appear in all Nightfire formats. Added alternate handling for Nightfire v1 files; prior to 2013-02-05 they have different, undocumented headers. There is an as yet undetermined break where additional fields were added to v1, including the 'Heat' field and some older files are missing certain MXX_Rad properties as well. Inserted log messages to identify where those breaks occur. Added ability to specify an Avro codec for compressing output files. Added check to ensure startDate is after the earliest available data (2012-09-01) and lastPulledDate is on or after startDate (in case startDate is changed after execution begins).