Metadata for "Height" variable field

The metadata defining the variable "Height" is incorrect.  The metadata 
states that "Height" is the altitude of the BOTTOM of the range bins.  
In fact, "Height" is the altitude to the MIDDLE of the range bins.  
This amounts to an interpreted difference of 150 meters, since the range 
bins are 300 meters in width.  The actual data values are unchanged, only 
interpretation of the altitude is different.  This pertains to all existing 
data produces from the MPL02 at the SGP site.

As the ingest procedure is moved from the ARM Experiment Center, the metadata
should be modified to reflect this difference in interpretation.  

If reprocessing of existing MPL02 data is recommended for some other reason, 
this change in the metadata should be propagated to the reprocessed data.

• base time in epoch(base_time)
• lon(lon)
• Height(height)
• Repetition Rate, or Trigger Frequency of the laser(pulse_rep)
• Detector Temperature(detector_temp)
• Binary data quality flag(cloud_base_height_dq_flag)
• Cloud base height (for first cloud above height threshold)(cloud_base_height)
• Filter Temperature(filter_temp)
• Voltage level which operates the A/D card and the detector(voltage_05)
• Aerosol volume backscattering coefficient at 355 nm(backscatter)
• Laser output energy per pulse(energy_monitor)
• Background signal(background_signal)
• Voltage level which operates the energy monitor(voltage_15)
• Voltage level which operates the thermistor(voltage_10)
• Instrument Temperature(instrument_temp)
• North Latitude(lat)
• Laser Temperature(laser_temp)
• Number of lidar pulses summed(shots_summed)
• -180.0 - +180.0(alt)
• Time offset from base_time(time_offset)