Support refining in infix form.

[TikhonJelvis]

Currently, if you want to refine a hole with an operator, you have to use prefix form. This means passing the operator in in parentheses ((+)) and having it applied like a normal function:

(+) _ _

It would be nice to support passing in the operator's name without parentheses (+) and getting it in infix form:

_ + _

It would also be nice to extend this to support backticks. Passing in mod should give us:

_ `mod` _