Handling of calibration data

[Pedro J. Aphalo]

Currently calibration data objects are created manually and included in the source distribution. This is a bug because these data objects contain functions, which to make this even worse are compiled from C++. Probably best solution is to build these data objects when the package is loaded. This should not add too much overhead, and could be also expanded to work with calibrations added by users.

[Pedro J. Aphalo]

No. Obvious and simple solution is to simply store the name of the function instead of the functions itself!!

[Pedro J. Aphalo]

Resolved by storing the name of worker functions as part of calibration data. This is certainly best for functions defined within the package itself, but not for user defined functions. Low level functions edited to accept both functions and function names.