Add error checking for publishTags command and rename to versions

[elcritch]

• Changed default behavior of command to print out new versions not yet published.
• Renamed from publishTags to versions since the commands intent is to find and then publish versions – tags are an implementation detail.
• Creating tags is done by nimble versions --create (or -c).
• Tags can be pushed by nimble versions --create --push (or -c -p).
• Only tags which were created are pushed with nimble cersions -c -p.
• All tags can be found, created, published with nimble versions --all (or -a).
• Non-monotonic historical versions are ignored and print an error.
• More with more recent versions historical versions take precedence over older versions. Older versions are marked as non-monotonic.