Decide if example should be written with global variables etc or with functions

Some examples and tutorial have the style of:

```julia
a = ...
b = ...

function do_something(a, b)
....
end

c = do_something(a,b)
```

Others have something like

```julia
function do_something(a, b)
....
end

function main()
a =
b =
c = do_something(a, b)
end
```

The first way is a bit easier to write "prose style" of documentation for but the second style is more "julian" and might perform slightly better. It's also a little bit arbitrary in the first style which parts should be in global scope and which should be in local.

Would be good to be consistent I guess.