add 'atags create' flag to non-destructively turn a named tag into an alias of another

[lun-4]

at the moment, if your tag inferrer created multiple tags for the same thing, they'll be dedicated tags with their own cores, and that makes sense because something like the regex tag inferrer doesn't have a neural network to assert if a tag looks like another, that requires human judgement.

$ atags search [...]
f82b1fe0b95d2d212c8ced6bb37bd4e25250a228d0781acdd4e18aa645d2207c 'a'
eb447ae1b5fe8434c6d31ae0ef00193b650e05f8ac83fa45466d9864217ca821 'b'
3565ed3c26ff3f8fe85178dd51472a8db0785e9b715503dea9663f8a47770878 'c'

say, b is actually a. you'd need to delete the named tag b (with atags remove --core eb447ae1b5fe8434c6d31ae0ef00193b650e05f8ac83fa45466d9864217ca821), removing all the file links to that core, then atags create --core f82b1fe0b95d2d212c8ced6bb37bd4e25250a228d0781acdd4e18aa645d2207c b (the core of a)

what i propose is that you can atags create --alias f82b1fe0b95d2d212c8ced6bb37bd4e25250a228d0781acdd4e18aa645d2207c b, atags would fetch the affected files, and create the necessary links back.