Add:
    - fix error handling.  In particular, ply_open_module gets it completely
      wrong (replies on errno instead of dlerror())

Add:
  - rotate boot.log per boot cycle (might be easiest to just fork/exec out to logrotate directly)

Remove:
  - Allow plymouth to be started from nash instead of
    the other way around

Add:
- clean up /var/run/plymouth before nash switchroots

There was a sort useless layer of indirection between the
window object and splash plugins.  It ended up with
functions like:

void
on_backspace (ply_splash_plugin_t *plugin)
{
  plugin->interface->on_backspace (plugin);
}

Since the individual plugins are aware of the window object
anyway, they can register their own on_backspace et al handlers
without going through the ply_splash_plugin_t layer.

Add:
- add expose handler for plugins to draw from.
  We need to reset some state every frame of the animation,
  so better to hide that.

Add:
- Add limited text support
- Make --ask-for-password take a prompt message
- consider making details plugin have stdin hooked
  up to the pty instead of tty so input works
- consider making details plugin go back to pretty
  plugin if user presses escape

The logic for line editing is a little complicated, so it's
best not to duplicate it across all the plugins.  Now we
manage it all from the window.  The plugins now access the
various editing events via there vtable, but that's an
extra layer of indirection that doesn't matter given that
we pass the window to the plugins anyway.  We should drop
that and just have the plugins register for edit events
directly.

We should really move a lot of the duplicate code between
the various splash plugins to the window code.  We also need
line editing support.