TODO

[Library]

    [X] Show min/max values
    [X] Change the axis order on the fly
    [X] Hide unwanted axes
    [X] Layers
        header {
            hide-layers = "layer1,layer2";
        }
        ...
        data {
            layer layer1 {
                axis1="foo", axis2="bar";
            }
            ...
        }
    [X] Can embed filters in the header:
        header {
            filter = "show plot > 50% on axis 3";
        }
    [X] Embed a logo in the image
    [X] Filter on frequency


Later (milestone 0.7)
=====================
    [ ] Add divider type to have several axes with points not reaching them
    [ ] Functions to specify variable behaviors:
        alias sec  1000 <- usec
        alias min  60 * sec
        alias hour 60 * min
        alias day  24 * hour
        alias timeline day

    [X] Fix number limit on the axis
        axes {
            4096 seqnum; # from 0 to 4096
        }

    [ ] Improve performances
    [ ] Add sublayers
    [ ] Animated GIF
    [ ] Curves can be used instead of straight lines upon request
    [ ] Mask layers to avoid drawing lines if they already belong to this mask: this will allow only new lines to be drawn and not the one we have seen already
    [ ] Allow rectangle selection filter