Exclude features with negative scores from context results.
Compare scores across indexes.
Merge pull request #188 from mapbox/context-score-fix

Exclude features with negative scores from context results
1.4.3
Merge branch 'master' into score-crossindex
Add test for cross-index scoring.
Utilize _sort strategically in verifymatch stage.
Merge pull request #189 from mapbox/score-crossindex

[semver bump] Compare scores across indexes
1.5.0
Merge branch 'master' into big-pants-rslow