add 2 options: ignore leading and/or trailing lines

[sitano]

We use customized formatting for leading lines and can't use whitespace without having disabled leading lines check. This patch adds 2 following options for customization that would be needed to further promoted to golangci-lint:

    -ignore-leading
       Do not check leading newlines

    -ignore-trailing
       Do not check trailing newlines

However, I did probably also have mode that can do:

f() {


     
return 1
}

->

f() {

return 1
}