refactor dplyr.frame() and lazy.frame() methods

[brownag]

I would like to avoid the "lazy.frame" terminology, and also "dplyr.frame" is not useful shorthand for tbl(). I was toying with the ideas, which now work fine, and now would like to have an API more consistent with the rest of the package.

• lazy.frame() will no longer be exported and will be renamed gpkg_table_pragma() -- this is useful information but not a substitute for table contents.
• dplyr.frame() will no longer be exported, it will be renamed internally and will be used inside gpkg_table() and gpkg_tables() unless new argument pragma is TRUE.
• gpkg_table() and gpkg_tables(): the new argument pragma=FALSE will require suggested package {dbplyr}, pragma=TRUE will use gpkg_table_pragma() instead of gpkg_table().
  • This is requiring the user to opt in to avoid the {dbplyr} dependencies rather than relying on what namespaces could be loaded to determine behavior (yuck)
  • gpkg_table() current behavior is to use dbGetQuery() to materialize full table in memory, which was not behavior of gpkg_tables(); "table" and "tables" will now be consistent and the old gpkg_table() code to make a table in memory will be available as gpkg_get_table() (or gpkg_collect_table() (?), or collect=TRUE argument to gpkg_table())

The lazy.frame/dplyr.frame functions will be removed from the namespace as I prepare for an initial release of gpkg v0.1.0.