Add separator classes

[daveredfern]

// =============================================
// Separator
// =============================================

.u-separator {
    border: 1px solid color(grey,light);
}

.u-separator-top {
    border-top: 1px solid color(grey,light);
}

.u-separator-bottom {
    border-bottom: 1px solid color(grey,light);
}

.u-separator-left {
    border-left: 1px solid color(grey,light);
}

.u-separator-right {
    border-right: 1px solid color(grey,light);
}

[gazjoy]

We need to keep trialing this, it may be added in the future, will revisit.

[daveredfern]

@gazjoy do you use anything like this yet? I've been using it often on sites.

[daveredfern]

Although with the idea of creating more rigid patterns this could be redundant?

[gazjoy]

@daveredfern this is in as part of #198