daily_synthesis: Daily AQ indicators
In jobonaf/pesco: Data fusion for air quality data

Functions to calculate daily Air Quality indicators

dailyCtm(data, statistic) 
dailyObs(data, statistic, pollutant, 
         Time="Time", Code="Code",
         others=c("Name","Municipality",
                  "Lat","Lon","Elev","Type"))
         
dailyStat(x, time, statistic, necess=0.75)

`data`	input hourly data. For `dailyObs`, a data frame; for `dailyCtm`, a list of 3 elements: coords coordinates, in a list of 2 x numeric matrix `[nx,ny]` y numeric matrix `[nx,ny]` time vector of `nt` POSIXct data concentration values in a 3 dimensions array `[nx,ny,nt]`
`statistic`	daily statistic to be used; possible values are "mean", "max" and "max8h" (daily maximum of the 8hr running mean)
`pollutant`	name of the column with pollutant concentations
`Time`	name of the column with time
`Code`	name of the column with station's code
`others`	vector of the names of the columns with station's static attributes
`x`	numeric vector of hourly data
`time`	vector of date-times as POSIXct
`necess`	fraction of valid hourly data needed in a day