calibrate: Calibrate trace gas data
In benfasoli/uataq: UATAQ Lab R Utilities

calibrate atmospheric trace gas data against several reference gas tanks.

1	calibrate(time, gasm, gask, auto = F, er_tol = 0.1, dt_tol = 18000)

`time`	POSIXct class timestamp, length n
`gasm`	numeric measured values, length n
`gask`	numeric gas concentration flag, length n. -10 for atmospheric observations, -99 for flush periods, or a positive value if sampling a known concentration
`auto`	if TRUE, stops calibration if the dataset ends with reference gas flow still active
`er_tol`	tolerated deviation from known value. e.g. 0.1 for 10 percent deviation from known
`dt_tol`	tolerated amount of time between observations, in seconds. If exceeded, will remove all atmospheric data until the next calibration