Filter the user name in the points top users table

We’ll use this to add the user’s rank.

See #180
Display a users rank in the top users table

Fixes #180
Document user_id arg for wordpoints_format_rank()

See #182
Remove errant spaces

See #180
Merge branch 'issue-180'
Include users without points in top users table

Previously, they were being inadvertently ignored if they had never had
any points transactions, because the metadata didn’t exist in the
database.

Includes unit tests.

Fixes #188
Merge branch 'issue-188'