Serde support

[rtbo]

Custom support for serialization and deserialization.
This is not a simple #[derive(Serialize, Deserialize)]. It is a hand crafted implementation to fit the plotive-js typescript definitions.
Therefore any figure written in JSON, YML or Javascript that follows those definitions can be parsed. non-provided fields will keep the default assignment. Ticks, strokes, colors etc. can either be deserialized from string, object or arrays per the typescript definitions.
Similarily, a figure can be automatically serialized into something that looks hand-written (all defaults props are ignored, those that can be simplified are etc.)

For example the minimal example serializes in YML as

title: Minimal Figure
plot:
  series:
    type: line
    x: x
    y: y

whereas implementation with #[derive(Serialize, Deserialize)] would look like the following which would also be required for deserialization:

plots:
  Plot:
    series:
      - Line: 
          x_data:
            SrcRef: x
          y_data:
            SrcRef: y
          name: null
          x_axis:
            Idx: 0
          y_axis:
            Idx: 0
          stroke:
            color: Auto
            width: 1.5
            pattern: Solid
            opacity: null
          marker: null
          interpolation: Linear
    x_axes:
      - id: null
        title: null
        side: Main
        scale: Auto
        ticks: null
        minor_ticks: null
        grid: null
        minor_grid: null
    y_axes:
      - id: null
        title: null
        side: Main
        scale: Auto
        ticks: null
        minor_ticks: null
        grid: null
        minor_grid: null
    x_axis_set: false
    y_axis_set: false
    title: null
    fill: null
    border:
      Box:
        color:
          Theme: Foreground
        width: 1.0
        pattern: Solid
        opacity: null
    insets: Auto
    legend: null
    colorbar: null
    annotations: []
title:
  text: Minimal Figure
  props:
    font_size: 20.0
    font:
      families:
        - SansSerif
      weight: 400
      width: Normal
      style: Normal
    fill:
      Theme: Foreground
    outline: null
    underline: false
    strikeout: false
  spans: []
size:
  w: 800.0
  h: 600.0
legend: null
fill:
  Solid:
    color:
      Theme: Background
    opacity: null
padding:
  Even: 20.0