Create a `rename()` function that is more specialized for an `epi_df`

[rachlobay]

Want to create our own rename() function such that if we rename a column corresponding to other_keys, we update the metadata accordingly (to have the updated name). For example, if we consider ex3 from here, if the user performs renamed_ex3 = ex3 %>% dplyr::rename(Pol = pol), then the metadata for renamed_ex3 should be updated to have Pol under $other_keys instead of pol. Also, if the user tries to change the name of either geo_value or time_value, should probably throw an error as those two are important to leave named as they are. Mentioned in Issues #192 and #194.

[brookslogan]

Related: #223. ?dplyr_extending might provide a way to limit the number of S3 implementations we have to provide.