Delete zero element method from writeblock! and readblock! (#153)

I suspect that these are not needed and they should be generic function definitions.

Author: felixcremer

src/diskarray.jl

@@ -12,15 +12,15 @@ abstract type AbstractDiskArray{T,N} <: AbstractArray{T,N} end
 
 The only function that should be implemented by a `AbstractDiskArray`. This function
 """
-function readblock!() end
+function readblock! end
 
 """
     writeblock!(A::AbstractDiskArray, A_in, r::AbstractUnitRange...)
 
 Function that should be implemented by a `AbstractDiskArray` if write operations
 should be supported as well.
 """
-function writeblock!() end
+function writeblock! end
 
 
 function allow_multi_chunk_access(a)