add tests for drop fx
stable sort preserves ties in orderby
update test fixtures
be clearer about whats going on
tests for garbage collector
Merge branch 'orderby-unit-test' of github.com:mapbox/vtfx-drop into orderby-unit-test
add garbage collector test
rename cleaner and drop tests
add unit test for linelabel
update comments on tests
update linelabel test to check id
Merge branch 'orderby-unit-test' of github.com:mapbox/vtfx into unit-test-dropkey