epiprocess 0.5.0

Potentially-breaking changes

• epix_slide, <epi_archive>$slide now feed f an epi_df rather than
  converting to a tibble/tbl_df first, allowing use of epi_df methods and
  metadata, and often yielding epi_dfs out of the slide as a result. To obtain
  the old behavior, convert to a tibble within f.

Improvements

• Fixed epix_merge, <epi_archive>$merge always raising error on sync="truncate".

Cleanup

• Added Remotes: entry for genlasso, which was removed from CRAN.
• Added as_epi_archive tests.
• Added missing epix_merge test for sync="truncate".

Full Changelog: https://github.com/cmu-delphi/epiprocess/commits/v0.5.0