autoFUN: A function to set up data ready to perform "auto" analysis.
In gmiskell/Cross_Auto_Functions: Error Scanning using Network or Historical Data

This function reformats the data relative to auto analysis, where site is held constant.

1	autoFUN(x, date, obs, ell = 3, sample.unit = "day", group = "site")

`date`	This is the data column.
`obs`	This is the column under observation.
`ell`	This sets the length of time backwards (in days) that should be considered as the auto proxy. Defaults to 3.
`sample.unit`	This classifies whether the analysis should consider data lags by days ('day', default), or by hours ('hour').
`group`	This is the id of each set of data being compared.