Fixed missing doc on macro "@~"

[yebai]

No description provided.

[tkelman]

@hayd why the close? The other PR was mistakenly against release-0.4 (do keep an eye out for PR's that unintentionally get opened that way). It would be good to squash these commits, and there's a decent chance we'll deprecate the ~ macro sooner or later, but for now this doesn't hurt.

[hayd]

oh, my bad!

Edit: Sorry about that!

[yebai]

I very much hope the ~ macro do not get deprecated, which is a low-maintenance feature but turns out to be really helpful. For example, this macro has been used to implement statistical formulas (e.g. x ~ Normal(0, 1)) in packages like DataFrames.

[tkelman]

See #11608 and JuliaStats/GLM.jl#116 - it's a non-extensible special case in the parser that "was introduced more-or-less for R compatibility" which isn't as important a design factor as it was early on when some of these features were first implemented. GLM and DataFrames could still use ~ for formula notation, but inside a macro DSL.

[vtjnash]

lgtm. would be nice to squash the commits when merging though

[vtjnash]

committed as 70477b7