Provide better access to the coordinates of a contour line about contour.jl

[darwindarak]

That looks good to me. Maybe we can also add a function to group the lines together:

function contour_lines(c::ContourLevel)
    N = length(c.lines)
    lines = Array(Vector{Float64}, Vector{Float64}, N)

    for (i, line) in enumerate(c.lines)
        lines[i] = coordinates(line)
    end

    return lines
end

[tomasaschan]

@darwindarak I'm not sure that's a good idea, since you loose some information in the process - given the result of that function, there's no way of knowing which, if any, of the included vertices are "false" ones, connecting the ends of two lines rather than specifying a surface. And since, given coordinates, it's not so hard to do if you do want it, we could just as well let the user handle it =)

I'll go ahead and add coordinates.

[tomasaschan]

Fixed by eb004be