v0.8.0

Volatility-surface calibration overhaul. This release adds a two-factor BNS
model, a double-Heston model (with optional jumps), Lewis and COS pricing
methods, and reworks the calibration package layout. Several module renames
and signature changes were made along the way: see Breaking changes below.

Breaking changes

Module renames.

• quantflow.sp.weiner is now quantflow.sp.wiener (typo fix). Update
  imports.
• quantflow.options.calibration is now a package, not a single module.
  Top-level imports keep working through the package __init__.py
  re-exports. Code reaching into the old quantflow.options.heston_calibration
  must switch to quantflow.options.calibration.heston.

ModelOptionPrice field rename. (#47)

• ModelOptionPrice.moneyness previously meant log(K/F). It now means
  standardised moneyness log(K/F) / sqrt(ttm), and the raw log-strike is
  exposed as a new field log_strike. Code reading option.moneyness and
  expecting a log-strike must switch to option.log_strike.
• get_intrinsic_value(moneyness=...) argument renamed to log_strike=....

New features

• BNS2: two-factor Barndorff-Nielsen & Shephard stochastic-volatility
  model with a single Brownian motion driving a convex combination of
  independent Gamma-OU variances and per-factor leverage. New section in the
  BNS calibration tutorial. (#54)
• DoubleHeston and DoubleHestonJ: two-factor Heston (with optional
  log-price jumps) and matching DoubleHestonCalibration /
  DoubleHestonJCalibration. (#46)
• Lewis and COS option-pricing methods: selectable via
  OptionPricingMethod, alongside the existing Carr-Madan / FFT path. (#47)
• CIR tutorial with PDF comparison example. (#49)

Improvements and fixes

• Heston calibration convergence fixes. (#45, #49)
• BNS calibration: dedicated BNSCalibration class extracted, characteristic
  exponent derivation cleaned up, broader test coverage. (#50, #51)
• OU module reworked: clearer Gamma-OU API, stronger tests for moments and
  the integrated Laplace transform. (#51)
• pricing_method_comparison example simplified; redundant time-comparison
  code removed. (#48)

Documentation and assets

• New logo set (favicon, lockup, marks, social banners) under
  docs/assets/logos/. (#53)
• New docs/mcp.md page covering the MCP server.
• Bibliography rebuilt from BibTeX via docs/bib2md.py; glossary expanded;
  mathjax tweaks for inline rendering. (#47, #49)
• Tutorial-writing instructions added at
  .github/instructions/tutorial.instructions.md.

Full changelog