Write test exercising case filtering
Add helper function to format filters
Print formatted filters before running tests
Skip tests with a mismatched filter
Don't count tests that were skipped
Fix warning about unused variable
Filters apply to tests instead of cases
Accept and parse filter command line option
Override test helper with command line flags
Parse filters in a more sane way
Clean up mix test options wrangling
Don't hold on to the filter after printing it
Ensure filter is always a list
Move filter parsing logic to a more testable place
Support exclusion of any tag key-value pair
Reverse filter match happy path to make more sense
Always run tests without matching tags
Dont require [] for keyword list operand in when/2
Dont add [] for last arg keyword lists in tuples, lists and when/2
Change typespec guards to keyword list

Previous syntax:
@spec fun(a) :: b when is_var(a) and is_subtype(b, [a])
New syntax:
@spec fun(a) :: b when a: var, b: [a]