Add a better story for API-based control

[storborg]

This could look like an AxiBot class with a higher-level interface for control. Something like:

path = svg.path.Path(...)
bot = AxiBot.connect()
bot.plot_path(path)

To test/demonstrate this, write a "clock" example which draws the current time as an analog clock once a minute or so.

[storborg]

One thing to note is that the suggested API above sort of departs from the pattern of pre-computed moves.

[storborg]

Actually, the use cases for realtime control are pretty obscure and limited, so I think it's probably better for the maintainability of the package to stick with precomputed jobs as the only use pattern.