Add ability to tag results and specify them

[johndgiese]

While working on image processing algorithms, a frequently encountered workflow is:

1. Run the HDAT suite
2. Show the results
3. Make some changes to the code
4. Run the suite
5. Show the results and possibly compare to the results from (1)
6. ... repeat

It is easy to get confused regarding which run is which. It would be nice to be able to tag the results of a particular hdat run ..., and to provide a way specify a particular tagged run in a result spec.

I think there should be a single result with a particular tag in a given store for a particular suite.

Maybe we should look at git for inspiration on the CLI, since developers are used to git.

Perhaps we can use symbolic links to implement the tags? Thus, resolving a resultspec for a tagged result would be checking for the existence of symbolic links with a particular name (I think this is what Git does).

[johndgiese]

Suite has set of cases
Case has a linear series of results

hdat run full-algorithm -t ideax
hdat show full-algorithm/case1/ideax
hdat show full-algorithm/ideax ??
hdat show full-algorithm -t ideax

[johndgiese]

This should be possible:
hdat run full-algorithm/case1 -t ideax
hdat run full-algorithm/case2 -t ideax
Although it is not particularly important.

This should not:
hdat run full-algorithm/case1 -t ideax
hdat run full-algorithm/case1 -t ideax # complains, but should provide the user a way to remove the old tag

[johndgiese]

FYI @russellkan I edited the previous comment