New implementations of Map and MapIndexed

[cekdahl]

The goal for this pull request was to figure out how to deal with level specifications. The following two functions have been implemented:

• Map
• MapIndexed

Map existed before, but it did not accept level specifications.

[corywalker]

Thanks for this change! I like how this implementation seems easily reusable with other parts which may require level specs. I have one small request before merging. Instead of the last commit to fix the build error, could we have something like this:

https://pastebin.com/2MtMqLma

I'm trying to move towards using constructors for these instantiations. The constructors will save headaches if we ever need to add a field that defaults to a certain value.

[cekdahl]

Great, fixed it.

[corywalker]

Thanks. I'll merge once I see the tests pass.