Simplify some current guidance to "have a blank line between multi-line blocks"?

Noticed when writing up https://github.com/domluna/JuliaFormatter.jl/issues/283 (see https://github.com/domluna/JuliaFormatter.jl/issues/283#issuecomment-687795763, related to #7), but better to discuss here :)

We currently have two rules:

• Use blank-lines to separate different multi-line blocks.
• Use line breaks between control flow statements and returns.

i wasn't sure how to translate the first one into a rule for a Formatter to follow, unless it just mean "have a blank line after end". If it can be translated to that, then the second one is just a special-case (assuming "control flow" here means only while.. end and if... end statements, which it seems to be, based on the example given).

I suggest we simplify these two rules in one. Below are some options for the new rule:

Option 1:

• Add a blank line after end in multi-line blocks

# Yes:
if foo
    println("Hi")
end

for i in 1:10
    println(i)
end

# No:
if foo
    println("Hi")
end
for i in 1:10
    println(i)
end

# Yes:
function foo(bar; verbose=false)
    if verbose
        println("baz")
    end

    return bar
end

# No:
function foo(bar; verbose=false)
    if verbose
        println("baz")
    end
    return bar
end

• Note that in this second example, the No case is currently listed as OK.

Option 2

• Add a blank line between multiple multi-line blocks

# Yes:
if foo
    println("Hi")
end

for i in 1:10
    println(i)
end

# No:
if foo
    println("Hi")
end
for i in 1:10
    println(i)
end

• Note we now longer give an opinion on the second example above (the blank line after end / before return)

Option 3

• Stop giving guidance on this

For what it is worth, i'd happily go with Option 3. In practice, i'm happy enough writing code that follows Option 2, but Option 1 seems a little too fussy to me.

Read this issue alongside JuliaFormatter.jl #283, its linked comment, and #7 to understand the current guidance and examples. Since no file or test is named, first locate the style-guide text, then document the agreed rule and update its examples once the open options have a decision.