get_pdat serves as a wrapper to the various pdat_ functions.
The names of the functions, which can include any user-defined functions in addition to those in the package, are specified in pdat_fun.
Those functions are queried for the availability of dataset; if one function provides it, the corresponding dataset is returned.
Leave dataset as NULL to list all datasets provided by the pdat_ functions.
# NOT RUN {library(CHNOSZ)
# list available datasets from pdat_CRC()get_pdat()
# the following produces the same result as pdat_CRC("JKMF10")get_pdat("JKMF10")
# }