v0.19.2

nanobook and the Python package move from 0.19.1 to 0.19.2, nanobook-risk from
0.8.0 to 0.8.1, and nanobook-rebalancer from 0.10.0 to 0.10.1. nanobook-broker
does not change and is not republished. The library code and the public API do
not change.

Added

• READMEs for nanobook-risk and nanobook-rebalancer. risk/README.md and
  rebalancer/README.md describe each crate and carry the disclaimer of the
  main README. The crates.io pages of both crates showed only the one-line
  package description and no disclaimer; they show the READMEs from this
  release on.

Fixed

• Install snippets in the README. Three snippets in README.md still said
  nanobook = "0.10.0". They now say nanobook = "0.19", and the crates.io
  page shows the new lines.
• test_recovery_time_typical_scenarios timed the file setup. The timer
  started before the test wrote its temporary audit log, so the 1 s limit also
  covered the file writes. A Windows CI runner took 1.55 s. The timer now starts
  just before reconstruct_state, and the 1 s limit is unchanged.
• Changelog gaps. The changelog had no section for 0.15.2 and no compare
  links for 0.18.1 and 0.19.0. It now has both.