Array.countBy and some fixes to List.countBy

[liboz]

Related to #184

[orcabot]

• docs/conceptual/list.countby['t,'key]-function-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/array.countby['t,'key]-function-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/collections.array-module-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.

[orcabot]

Hi! I'm your friendly content validation bot. For this PR to be labeled as ready-to-merge, you'll need at least 2 comments from our designated community approvers containing the magic phrase LGTM (Looks good to me also works, for those of us that are really verbose).

@dend @KevinRansom @cartermp @thedanfernandez @dsyme - please validate this PR.

[orcabot]

• docs/conceptual/list.countby['t,'key]-function-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/collections.array-module-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/array.countby['t,'key]-function-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.

[dend]

This LGTM as long as @cartermp can validate the code.

[cartermp]

Suggested change:

let printArray anarray =
    anarray |> Array.iter (printf "%A ")
    printfn ""

Generally avoiding semicolons is a good thing for samples, as they're hard for people to catch when reading.

[orcabot]

• docs/conceptual/array.countby['t,'key]-function-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/list.countby['t,'key]-function-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/collections.array-module-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.

[orcabot]

• docs/conceptual/list.countby['t,'key]-function-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/array.countby['t,'key]-function-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/collections.array-module-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.
• docs/conceptual/collections.list-module-[fsharp].md - Article contains URLs. Make sure that non-Microsoft URLs are using the aka.ms shortener.

[cartermp]

LGTM. Thanks, @liboz!