Release 0.8.0.0: interactive plots!

This release brings two new toolkits:

• Added a new toolkit, bokeh. This toolkit can take advantage of the new HTML interactive output.
• Added a new toolkit, plotsjl.

One MAJOR addition: interactive plots!

• Added a new output format, HTML, to produce interactive plots. Not all renderers support it. You can try with Plotly/Python, Plotly/R, or Bokeh as follows:

```{.plotly_python format=html}
import plotly.express as px
df = px.data.election()
fig = px.scatter_ternary(df, a="Joly", b="Coderre", c="Bergeron")
```

Other small changes:

• Separated the detailed information from README.md and into a proper MANUAL.md. This is now the information which will be shown with pandoc-plot --manual.
• Exposed the pandoc-plot version via Text.Pandoc.Filter.Plot.pandocPlotVersion.