75 add data

[jmbarbone]

related to #75

I didn't do anything to the actual write_data() and write_datatable() functions. These aren't incorporated into the R6 object, but instead called within them and a wrapper created to call that. This means we can keep working off the write_*() functions until they're reworked to be called directly from the workbook.

I'm also thinking about if it makes sense to use $add_data_table() or just change that to $add_table(). That would be an easy change.

[JanMarvin]

Looks good, I'll make a run tomorrow. Not sure about calling it add_data(), write seems more natural, but that's your decision and I understand your augmentation.

[jmbarbone]

Not sure about calling it add_data(), write seems more natural, but that's your decision and I understand your augmentation.

Technically I guess we're writing everything because it's modifying the xml? This does at least keep it consistent with the other add_/get_/set_ etc prefixes.

[JanMarvin]

As I said, I understand your reason, but whenever one processes data in R for the purpose of storing it, the functions that do this are called write.... So we sacrifice principles of the language for consistency, I just wanted to note that. On the other hand, dbplyr also does this with copy_to(), so probably I'm just being too intellectually inflexible.

I've updated the README.