added subway-entrance-24 and -12, both in progress
added subway-entrance-18 and -24, in progress
modified subway-entrance-18.svg
updated subway-entrance-12.svg
finalize subway-entrance-12.svg
finalized subway-entrance-24.svg and subway-entrance-18.svg
renamed all svgs from subway-entrance to entrance
Merge branch 'gh-pages' into subway-entrance
updated maki.json with entrance icon, rendered all entrance icon  files
Merge pull request #137 from mapbox/subway-entrance

Add Entrance icon