some array docs, backup show?

Author: rayegun

docs/src/arrays.md

@@ -56,20 +56,19 @@ The usual AbstractArray and SparseArray indexing capabilities are available. Inc
 !!! danger "Indexing Structural Zeros"
     When indexing a `SparseMatrixCSC` from `SparseArrays` a structural, or implicit, zero will be returned as `zero(T)` where `T` is the element type of the matrix.
 
-    When indexing a GBArray structural zeros are instead returned as `nothing`. 
+    When indexing a GBArray structural zeros default to `nothing`.
     While this is a significant departure from the `SparseMatrixCSC` it more closely matches the GraphBLAS spec,
     and enables the consuming method to determine the value of implicit zeros. 
 
     For instance with an element type of `Float64` you may want the zero to be `0.0`, `-∞` or `+∞` depending on your algorithm. In addition, for graph algorithms there may be a distinction between an implicit zero, indicating the lack of an edge between two vertices in an adjacency matrix, and an explicit zero where the edge exists but has a `0` weight.
 
-    Better compatibility with `SparseMatrixCSC` and the ability to specify the value of implicit zeros is provided
-    by `SuiteSparseGraphBLAS.SparseArrayCompat.SparseMatrixGB` array type.
+    However, many functions outside of GraphBLAS will not work when they index into an `AbstractArray` and get `nothing`. 
 
 ```@repl mat
 A = GBMatrix([1,1,2,2,3,4,4,5,6,7,7,7], [2,4,5,7,6,1,3,6,3,3,4,5], [1:12...])
 SparseMatrixCSC(A)
 A[4]
-A[1,2]
+A[1,2] 
 A[[1,3,5,7], :]
 A[1:2:7, :]
 A[:,:]

src/abstractgbarray.jl

@@ -507,6 +507,12 @@ function Base.show(io::IO, ::MIME"text/plain", A::AbstractGBArray) #fallback pri
     gxbprint(io, A)
 end
 
+function Base.show(io::IO, mime, A::AbstractGBArray) #fallback printing
+    gxbprint(io, A)
+end
+
+
+
 function Base.getindex(
     A::AbstractGBMatrix, i::Union{Vector, UnitRange, StepRange, Number, Colon}, j::Union{Vector, UnitRange, StepRange, Number, Colon};
     mask = nothing, accum = nothing, desc = nothing