Support aliases like R-next and R-devel on Windows and macOS as well

[gaborcsardi]

Maybe even R-oldrel.

They could be updated manually:

rig alias add
rig alias update

macOS

• rig add add alias if installed by alias.
• rig rm remove alias to removed version.
• rig list should include aliases.
• rig list --json should include aliases.
• rig default <ver> should work with aliases.
• rig rm <ver> should work with aliases.
• rig rstudio <ver> should work with aliases.
• rig system subcommands should work with aliases.
• rig alias list to list current aliases.
• rig alias update to update aliases according to the R versions API.
• rig system make-links should update aliases.

Windows

• rig add add alias if installed by alias.
• rig rm remove alias to removed version.
• rig list should include aliases.
• rig list --json should include aliases.
• rig default <ver> should work with aliases.
• rig rm <ver> should work with aliases.
• rig rstudio <ver> should work with aliases.
• rig system subcommands should work with aliases.
• rig alias list to list current aliases.
• rig alias update to update aliases according to the R versions API.
• rig system make-links should update aliases.

Linux

• rig add add alias if installed by alias.
• rig rm remove alias to removed version.
• rig list should include aliases.
• rig list --json should include aliases.
• rig default <ver> should work with aliases.
• rig rm <ver> should work with aliases.
• rig rstudio <ver> should work with aliases.
• rig system subcommands should work with aliases.
• rig alias list to list current aliases.
• rig alias update to update aliases according to the R versions API.
• rig system make-links should update aliases.

[gaborcsardi]

• We could add aliases at install time. Every time we install a version using an alias, we add that as an alias. E.g. rig add next will add R-next. When we call rig add next again, then we update the alias. (It might refer to a new version now.)
• We can also update aliases with rig alias update.
• rig alias update can have an option to add "standard" aliases: oldrel, next, release, devel.

[gaborcsardi]

OTOH, it is probably not worth adding a new rig alias command for this. rig ls already lists the aliases, and rig system make-links could also update the aliases, unless opt out.

[gaborcsardi]

I'll update rig system make-links later.

[gaborcsardi]

Actually, I like this as it is. It would be weird to update aliases from system make-links, if no new version is installed.

Instead we could have a rig system update-aliases subcommand, but we could wait with that until we have generic, user-defined aliases.