fixup! Add phlcon_user.UsernamePhidCache.get_username()
WIP: add phlcon_user.get_username_phid
Revert "WIP: add phlcon_user.get_username_phid"

This reverts commit c9fabe32cc007422789a7439683d37aaf81ac92d.
exercise_arcyon: add task-query with user params

Exercise 'arcyon task-query' with some user params to increase the
coverage of task-query.

Test Plan:
$ ./testbed/arcyon/exercise_arcyon.sh
Refactor, add '_from_[phid,username]' to cache fns

Make it easier to use the phlcon_user.UsernamePhidCache accessors by
putting the name of the input they expect directly in the function name.
This makes the calling code easier to validate and makes way for
broadening the scope of UsernamePhidCache.

Fix up places where the longer names make breaks to the 80 char rule.

Test Plan:

Make the rename using rope, git grep for the old names to make sure none
got left behind. Manually review the diffs to make sure no unexpected
substitutions were made.

Update doc and exercise most affected code with
$ ./precommit.sh
Add phlsys_dictutil.invert()

Sometimes it's useful to swap keys and values in a dictionary to provide
a reverse mapping.  Wrap up this snippet in a friendly function that
should make calling code easier to read.

Add doctest example.

Test Plan:

Update doc and usual tests
$ ./precommit.sh
Refactor, use phlsys_dictutil.invert

Increase readability by using phlsys_dictutil.invert to swap keys and
values in dicts instead of spelling it out in full.

Test Plan:
$ ./precommit.sh
WIP: rename "results"