add labelgrid to index.js
first draft of labelgrid fx ref #2
clean up
labelgrid is called labelgrid
add tests, test fixtures
update labelgrid test, test fixture to be more dramatic
sketch of order by
sort asc or desc
update tests
only complain that order field doesnt exist if it's set
Merge pull request #7 from mapbox/labelgrid

labelgrid
strip our orderby bits into their own fx
add orderby fx
register orderby in index.js
first draft of order by fx
update labelgrid test fixtures
add orderby test, test fixtures
clean up
better order by
update test fixtures