Documentation of retained metadata for `read_sas`, `read_xpt`, `write_xpt`

[kaz462]

Would it be possible to document a list of retained metadata when using read_sas, read_xpt, write_xpt? to help users understand which metadata is kept through read, as well as the attributes that can be customized during write. Thank you!

[botsp]

Yes, hope it can keep the Sort Information when sas dataset is imported into R;