Change the SW clean-up (#116)

We can just remove the SW for our scope.

Older Safari: Handle speech sample rate errors, reuse audio context (#…

…111)

- Workaround for #110 where we've observed that the sample rate of 19000 isn't supported. We'll aim to increase the sample rate in a separate PR but this will at least mean the simulator isn't put in a bad state.
- Reuse the audio context created after the user interaction, as there are limits to how many you can create on Safari 13 (4 in my BrowserStack testing). I think we always intended to do this, but careful review needed as this is a more significant change than I was anticipating. We already had clean up code for the nodes when the board stops. We never cleaned up the context. So I think we were assuming it lived forever. If this doesn't work out then an alternative is to try closing the old one before creating the new one.

Increase asyncify stack size (#106)

Pick the first power of two where we fail with a pystack exhausted
error in MicroPython rather than an asyncify-related error.

Add an example to the demo that finds the max stack size.

Fix interrupting input() (#103)

Handle pending KeyboardInterrupt.

Closes #100

Fix Safari AudioContext initialisation. (#99)

Current version seem to require the user interaction to be on the stack
when creating/resuming the context.

Switch to a single context and resume it if it starts suspended.

Add some clean-up so we can keep the single context for the lifetime of
the app (across stop/start).

Closes #97

Install a fixed build of emscripten. (#96)

We've not seen issues using latest but it's likely to break us
eventually.

Closes #15

Fix for reset/panic overriding the user's stop take 2 (#91)

This reverts commit 9d7c834 with an additional changes to avoid introducing #90.

Closes #86

Revert "Fix for reset/panic overriding the user's stop (#88)"

This reverts commit 7c5b2e6.

Fix for reset/panic overriding the user's stop (#88)

Switch to an enum to make the possible states easier to follow and so we
can check we're in the default state before committing to a reset or
panic.

Closes #86

Fail in a controlled way for asm_thumb use. (#82)

Closes #81