Implement `to_ccdef()` function to output WFDB data to CCDEF/HDF5 Critical Care Data Format

[tompollard]

This needs more thought/discussion, but I wanted to make a note before I forget. If possible it would be helpful if we could introduce a function that would allow WFDB data to be easily outputted to the CCDEF/HDF5 Critical Care Data Format.

The general suggestion is that we could load a record using the WFDB package and then output to CCDEF with a to_ccdef() method.

The function would be useful for the CHoRUS project (https://chorus4ai.org/) which requires data in both WFDB and CCDEF formats. For more information on the CCDEF format, see: https://ccdef.org/.