added pmap method for arrays, with type/shape of result the same as map

[gajomi]

Implements array methods for pmap so that the shape and eltype of return type are the same as those from map (see issue #14265).

Example:

julia> a = rand(2,2)
2x2 Array{Float64,2}:
 0.745134  0.94089 
 0.382871  0.809724

julia> b = map(abs,a)
2x2 Array{Float64,2}:
 0.745134  0.94089 
 0.382871  0.809724

julia> c = pmap(abs,a)
2x2 Array{Float64,2}:
 0.745134  0.94089 
 0.382871  0.809724

Further tests for n-ary functions in PR body.

[gajomi]

Is there anything that should be done (or undone) to get this merged?

[tkelman]

@amitmurthy did you implement this recently?

sorry this never got revewed @gajomi

[amitmurthy]

shape works now, type and leveraging the different map implementations is yet to be done.

[vtjnash]

Moved to JuliaLang/Distributed.jl#33