v0.1.2

Added

• The market types serialise under the serde feature: PriceAmount,
  OrderBookSide, OrderBook, OrderBookTop and OrderBookDiff. A book
  snapshot now round trips whole, where before only Dec did.
• OrderBook::is_consistent — every level valid, each side ordered the way its
  slot requires, no price held twice, and a spread above zero. A book built
  through set holds this by construction, so check it on one that arrived
  another way: deserialised from a snapshot, or assembled by hand.
• Display honours the format spec. A precision rounds to exactly that many
  places, halves away from zero, padded with zeros past Dec::SCALE; width,
  fill, alignment, 0 and + behave as they do on the built-in numeric types.
  Bare {} is unchanged, and still compiles to what it did before. The
  rounding runs on the digits rather than through a Dec, so a carry out of
  the range still renders: format!("{:.0}", Dec::MAX) is
  170141183460469231732, a number Dec cannot hold and round_dp answers
  with Dec::NAN.
• A benchmark and docs site at https://troy.quantmind.com, carrying the full
  benchmark set, the order book numbers, the digit and depth sweeps and the
  design docs. make site builds it, make site-dev serves it locally.

Removed

• make bench-page, which rendered a single page from the snapshot. make site builds the whole site instead.