Allow .~ infix operator

[cscherrer]

~ is standard notation for statistical distributions, for example x ~ Normal(0,1). Because of this, it's a natural choice for probabilistic programming DSLs like Soss.jl and Turing.jl.

It would be convenient to allow this notation to be broadcast in the usual way, for example allowing x .~ Normal(0,1). But this currently seems to be disallowed:

julia> :(x .~ Normal(0,1))
ERROR: syntax: missing comma or ) in argument list

@StefanKarpinski suggested I open an issue to request this be changed:
cscherrer/Soss.jl#14 (comment)

Thank you!