Provide function for calculating local barometric pressure

[jbeaulie]

Ideally investigators will measure barometric pressure at the sampling site; however, it is not uncommon for investigators to pull this information from an online database (i.e. www.weatherunderground.com) for a local weather station. It is important that investigators realize that BP data from most online sources is corrected to sea level, whereas the dissolved gas calculations require a calculation of local BP. I think it would be helpful if we could provide a function to convert sea level corrected BP to local BP. I believe the function only requires altitude.

[kcawley]

This existing NEON package might be helpful for pulling data from nearby met stations. https://cran.rstudio.com/web/packages/metScanR/