Allow for describe to operate over an entire Matrix

[this-josh]

As discussed here currently if you pass a matrix to describe you get an error from quantile!

julia> describe(reshape(collect(1:100), (10, 10)))
ERROR: MethodError: no method matching quantile!(::Matrix{Int64}, ::Vector{Float64}; sorted=false, alpha=1.0, beta=1.0)
Closest candidates are:
  quantile!(::AbstractArray, ::AbstractVector, ::AbstractArray; sorted, alpha, beta) at /Applications/Julia-1.7.app/Contents/Resources/julia/share/julia/stdlib/v1.7/Statistics/src/Statistics.jl:936
  quantile!(::AbstractVector, ::Union{Tuple{Vararg{Real}}, AbstractArray}; sorted, alpha, beta) at /Applications/Julia-1.7.app/Contents/Resources/julia/share/julia/stdlib/v1.7/Statistics/src/Statistics.jl:953
Stacktrace:
 [1] quantile(itr::Matrix{Int64}, p::Vector{Float64}; sorted::Bool, alpha::Float64, beta::Float64)
   @ Statistics /Applications/Julia-1.7.app/Contents/Resources/julia/share/julia/stdlib/v1.7/Statistics/src/Statistics.jl:1070
 [2] quantile(itr::Matrix{Int64}, p::Vector{Float64})
   @ Statistics /Applications/Julia-1.7.app/Contents/Resources/julia/share/julia/stdlib/v1.7/Statistics/src/Statistics.jl:1070
 [3] summarystats(a::Matrix{Int64})
   @ StatsBase ~/.julia/packages/StatsBase/pJqvO/src/scalarstats.jl:915
 [4] describe(io::Base.TTY, a::Matrix{Int64})
   @ StatsBase ~/.julia/packages/StatsBase/pJqvO/src/scalarstats.jl:943
 [5] describe(x::Matrix{Int64})
   @ StatsBase ~/.julia/packages/StatsBase/pJqvO/src/scalarstats.jl:941
 [6] top-level scope
   @ REPL[3]:1

I made a small change which vectorises a matrix and provides a description for the whole matrix.

julia> describe(reshape(collect(1:100), (10, 10)))
Summary Stats:
Length:         100
Missing Count:  0
Mean:           50.500000
Minimum:        1.000000
1st Quartile:   25.750000
Median:         50.500000
3rd Quartile:   75.250000
Maximum:        100.000000
Type:           Int64

In the future a dims argument could be useful.

[nalimilan]

Thanks! However I think we'd better change quantile in Statistics to accept any AbstractArray, rather than working around this limitation downstream. Would you make a PR in Statistics?

[JoshKImperial]

Sure, I'll look into this making a PR in Statistics