Create Files for the first R programming assignment

pollutantmean is an R file for calculating the mean of a given pollutant
across 1:332 independent sensor output files (or any subset thereof)
from across the US ignoring any missing values by first taking the mean
of each sensor in question. It contains one function with signature:
pollutantmean(directory, pollutant, id = 1:332)

complete is an R file for calculating the number of "complete"
observations in 1:332 independent sensor output files (or any subset
thereof) from across the US. It contains one function with signature:
complete(directory, id = 1:332)

corr is an R file for calculating the correlation between the two
pollutants for each sensor with the number of complete readings above
the threshold value and returns a numeric vector of correlations. It
contains one function with signature: corr(directory, threshold = 0)