v0.3.0

• Currying operators curry() and curry_fn() are introduced (#10). Notably,
  curry_fn() supports quasiquotation, which enables more easily inspectable
  functions. For example:

  compare_to <- curry_fn(target, x ~ identical(x, QUQ(target)))
  print(compare_to("this"))
  #> function (x)
  #> identical(x, "this")

• fn() now accepts closures as part of the body. In particular, nested calls
  of fn() can be unquoted, e.g., fn(x ~ !!fn(y ~ !!fn(z ~ x + y + z)))
  yields function(x) function(y) function(z) x + y + z.

• Literal unquoting operators QUQ(), QUQS() now resolve to their
  bang-operator forms (!!, !!!), rather than their functional aliases
  (UQ(), UQS()), as these aliases are slated for potential deprecation in
  rlang (#9). rlang::UQE() has already been axed, so QUQE() is gone too.