get.local.lw.datums: Get local low water datums
In acgoodman/wlTools: Tools for handling water pressure and salinity data

Calculates low and lower high water datums from a short term tide station using a NOAA reference station

1	get.local.lw.datums(time.series, station, out.dir, by = "overall")

`time.series`	a csv file that contains the fields DateTime representing DateTime in excel format and Level representing NAVD water levels in meters
`station`	the numeric ID of the NOAA reference station
`out.dir`	an optional output directory in which to save results
`by`	whether to calculate the datums overall or by year. It is almost always most appropriate to calculate it by 'overall'.