Resolve or silence documentation warnings for epi_archive

[brookslogan]

Attempting to devtools::document() the package results in several warnings regarding the docstrings for epi_archive:

Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:80] undocumented R6 method: `print`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:80] undocumented R6 fields: `DT`, `geo_type`, `time_type`, `additional_metadata`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:191] argument `max_version` undocumented for R6 method `as_of()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:191] argument `min_time_value` undocumented for R6 method `as_of()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:235] argument `y` undocumented for R6 method `merge()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:235] argument `...` undocumented for R6 method `merge()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:235] argument `locf` undocumented for R6 method `merge()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:235] argument `nan` undocumented for R6 method `merge()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `f` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `...` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `n` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `group_by` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `ref_time_values` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `time_step` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `new_col_name` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `as_list_col` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `names_sep` undocumented for R6 method `slide()`
Warning: [/home/fullname/files/tooling/epiprocess/R/archive.R:266] argument `all_rows` undocumented for R6 method `slide()`
Writing NAMESPACE

Investigate:

• which are intentional due to the complications of documenting dual R6-S3 classes, and should be silenced if possible (so we can easily notice real documentation warnings for other things)
• which require just a little copying/shifting around of content or placing appropriate roxygen tags
• which require describing actually-undocumented functions/parameters (probably the most work)

and implement the appropriate changes.

[dajmcdon]

I have a fix for most of this on my fork.

I lied. I haven't fixed these but R-CMD-Check doesn't care.

[brookslogan]

Closing this as a duplicate of #132, as there are more specific suggestions about how to resolve this there.