r4sub 0.1.0

• Initial CRAN release.
• core_packages(): list the 6 auto-attached ecosystem packages.
• r4sub_packages(): show all packages with version and attachment status.
• r4sub_status(): check which ecosystem packages are installed.
• r4sub_conflicts(): detect function name conflicts with other loaded packages.
• r4sub_news(): print NEWS for each ecosystem package.
• r4sub_cite(): print citation information for regulatory or academic use.
• Startup message can be suppressed with options(r4sub.quiet = TRUE).