split raw reading/ merging to prep for integration with OA

[rBatt]

If trawlData::read.trawl doesn't merge at the same time it reads, I can use the trawlData functions in the OceanAdapt workflow.

First step is to split the read.__ functions into reading raw and merging (merging bio data with stratum info, e.g.).

Next step is to export and document the raw reading functions.