Field change: exposed-modules to exported-modules

[mgold]

Related to elm/compiler#1124, we should be more precise about the definition of exposed vs. exported. The exposed-modules field of elm-package.json should be renamed exported-modules (in a backwards compatible way). This will clarify the distinction between exporting a module for others and importing it with values exposed for your own use.

[evancz]

I kind of think this distinction is weird. It does not feel like it has a clear uniform meaning across all the things you are interested in. Overall, I'm not sure if making a subtle weird distinction is worth the confusion it'll cost in having to tell everyone the subtle weird distinction so they can remember which is which.

Anyway, point is elm-lang/elm-make#59 has discussion of this, so now there's a link and it'll be in the feed when I go to work on that stuff. I don't want to cause a side-discussion, so please do not add additional comments there. The backlink will work!