Pfhedge

* BUG: Fix BS European price put (238) (Thank you, masanorihirano !)

* ENH: Beautify `repr` of instruments using `extra_repr` (237)

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* API: Rename `volatility` to `sigma` in Brownian (close 210) (231)

* DOC: `WhalleyWilmott`: Add Note that backward could generate `nan` (close 213) (232)

* DOC: Add intersphinx and copybutton to docs (233)

* CHORE: Create GitHub Action publish.yml (230)

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* DOC: Add docs of `Derivative.list()` to each derivative (226)

* DOC: Fix typo (225)

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* ENH: Enable hedging with derivative (133) (219)

* DOC: Clarify "Otherwise:" in Clamp 218

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* BUG: Fix `time_to_maturity` mismatch (close 211) (214)

* ENH: Add `VarianceSwap` (close 127) (207)

* DOC: Fix code blocks in docstrings (199)

* MAINT: Use `disable` in `tqdm` (209)

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