Add parse_args() function

[kdpsingh]

This is not high priority at all (have other issues to address first) but I want to create a new parsing function that will solve the problem of intermixing named with positional arguments. In R, this is fairly common and R has a specific behavior.

We would probably call this as parse_args([:x, :y, :z], exprs...), where the vector indicates the R-style position of the arguments on the macro, and this would parse and return the arguments in the correct order. This is kind of like the match.call() function in R and will ultimately end up in the TidierTools package.

Note to self: we need to add a :dots option to handle ... arguments. Anything after the :dots must be a named argument.