ropensci/targets: Integration with {crew}

targets 1.0.0 targets is moving to version 1.0.0 because it is significantly more mature than previous versions. Specifically, tar_make() now integrates with crew, which will significantly improve the way targets does high-performance computing going forward. All other functionality in targets has stabilized. There is still room for smaller new features, but none as large as crew integration, none that will fundamentally change how the package operates. Major improvements Support distributed computing through the crew package in tar_make() (#753). crew itself is still in its early stages and currently lacks the launcher plugins to match the clustermq and future backends, but long-term, crew will be the predominant high-performance computing backend. Minor improvements Add a new store_copy_object() to the store class to enable "fst_dt" and other formats to make deep copies when needed (#1041, @MilesMcBain). Add a new copy argument to allow tar_format() formats to set the store_copy_object() method (#1041, @MilesMcBain). Shorten the output string returned by tar_format() when default methods are used. Add a change_directory argument to tar_source() (#1040, @dipterix). In format = "url" targets, implement retries and timeouts when connecting to URLs. The default timeout is 10 seconds, and the default retry interval is 1 second. Both are configurable via tar_resources_url() (#1048). Use parallelly::freePort() in tar_random_port(). Rename a target and a function in the tar_script() example pipeline (#1033, @b-rodrigues). Edit the description