Rename *Aux helper classes to *Curried

[fthomas]

We currently have a few helper classes that have an Aux suffix
for emulating currying type parameters. These helper classes have
an apply method which allows some type parameters of a function
to be inferred while others need to be specified. @tpolecat has
nice explanation of this trick here:

http://tpolecat.github.io/2015/07/30/infer.html

Unfortunately the suffix Aux is an overloaded term that is most
prominently used to provide terser syntax for type refinements, e.g.:

type Aux[F[_], A, B] = Coyoneda[F, A] { type Pivot = B }

I'm wondering if we should use Curried instead of Aux for classes
that enable type parameter currying. This could make the purpose of
those classes clearer to those who are unfamiliar with this trick.

[codecov-io]

Current coverage is 76.15%

Merging #577 into master will increase coverage by +0.45% as of e428a1d

@@            master    #577   diff @@
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  Files          157     158     +1
  Stmts         2165    2172     +7
  Branches        68      68       
  Methods          0       0       
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+ Hit           1639    1654    +15
  Partial          0       0       
+ Missed         526     518     -8

Review entire Coverage Diff as of e428a1d

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[ceedubs]

I don't have any very strong opinions on this, but it seems reasonable to me 👍

[milessabin]

I've used Aux as a suffix for this purpose, but I agree that it is very overloaded, and the primary use is, as @fthomas says, as terser syntax for refinements.

I think that this is about partial application rather than currying however, so maybe Partial or PartiallyApplied as a suffix? It's not expected that a user would have to name these types explicitly, so a little verbosity shouldn't be an issue.

[travisbrown]

I've used -Helper or just -er for these things, in an attempt to make it clear that they're just a type inference hack and have nothing interesting going on, but I like -PartiallyApplied a lot better. I definitely agree that -Aux should be changed.

[fthomas]

👍 for PartiallyApplied

[ceedubs]

👍

[stew]

👍

[julienrf]

Conversely, do you think we should rename Aux to Uncurried?