Adds changelog for v4.2.0. (#529)

This pull request adds a changelog for `v4.2.0`. The changelog is based
on the following auto-generated summary of merge commits generated by
GitHub:

```
## What's Changed

* bug-fix: Numpy ValueError when cheking empty list equality by @ajadczaksunriselabs in #459
* bug-fix: Pandas set indexing error by @ajadczaksunriselabs in #460
* fix for /issues/452 by @tecamenz in #465
* Use numpydoc to render documentation by @SnoopJ in #472
* build(deps): bump readthedocs-sphinx-search from 0.1.1 to 0.3.2 in /docs by @dependabot in #477
* Update style by @bemoody in #482
* Fix NaN handling in Record.adc, and other fixes by @bemoody in #481
* Set upper bound on Numpy version (numpy = ">=1.10.1,<2.0.0"). Ref #493. by @tompollard in #494
* Update actions to use actions/checkout@v3 and actions/setup-python@v4. by @tompollard in #495
* Fix: Indent code to ensure 'j' is within for-loop in GQRS algorithm by @tompollard in #499
* Add write_dir argument to csv_to_wfdb. Fixes #67. by @tompollard in #492
* Fix warnings by @cbrnr in #502
* README improvements by @bemoody in #503
* Change in type promotion. Fixes to annotation.py by @tompollard in #506
* Use uv by @cbrnr in #504
* Change in type promotion. Fixes to _signal.py by @tompollard in #507
* Test round-trip write/read of supported binary formats by @bemoody in #509
* Corrected typo and extended allowed types for MultiSegmentRecord by @agent3gatech in #514
* Allow expanded physical signal in `calc_adc_params` by @briangow in #512
* Add capability to write signal with unique `samps_per_frame` to `wfdb.io.wrsamp` by @briangow in #510
* Fix selection of channels when converting to EDF by @SamJelfs in #519
* Change in type promotion introduced in Numpy 2.0. Fixes to edf.py. by @tompollard in #527
* Bump dependencies for NumPy 2 compatibility by @cbrnr in #511
* Bump version to v4.2.0 and update notes on creating new releases by @tompollard in #497

## New Contributors

* @ajadczaksunriselabs made their first contribution in #459
* @tecamenz made their first contribution in #465
* @SnoopJ made their first contribution in #472
* @dependabot made their first contribution in #477
* @agent3gatech made their first contribution in #514
* @SamJelfs made their first contribution in #519

**Full Changelog**: v4.1.2...v4.2.0
```

docs/changes.rst

@@ -5,6 +5,40 @@ This page lists recent changes in the `wfdb` package (since version 4.0.0) that
 
 .. _development repository: https://github.com/MIT-LCP/wfdb-python
 
+Version 4.2.0 (Jan 2025)
+-----------------------------
+
+**Add support for Numpy 2.0**
+  Fixes were added to address [changes to type promotion](https://numpy.org/devdocs/numpy_2_0_migration_guide.html#changes-to-numpy-data-type-promotion) that led to overflow errors (e.g. https://github.com/MIT-LCP/wfdb-python/issues/493). 
+
+**Fix UnboundLocalError in GQRS algorithm**
+  Fixes the GQRS algorithm to address an `UnboundLocalError`.
+
+**Support write directory in `csv_to_wfdb`**
+  `write_dir` can now be specified when calling `csv_to_wfdb`.
+
+**Use uv for for package management**
+  Moves package management from poetry to uv.
+
+**Fix misordered arguments in `util.lines_to_file`**
+  Fixes misordered arguments in `util.lines_to_file`.
+
+**Allow signals to be written with unique samples per frame**
+  Adds capability to write signal with unique samps_per_frame to `wfdb.io.wrsamp`.
+
+**Allow expanded physical signal in `calc_adc_params`**
+  Updates `calc_adc_params` to allow an expanded physical signal to be passed. Previously only a non-expanded signal was allowed.
+
+**Allow selection of channels when converting to EDF**
+  Fixes the `wfdb-to_edf()` function to support an optional channels argument.
+
+**Migrates Ricker wavelet from SciPy to WFDB after deprecation**
+  The Ricker wavelet (`scipy.signal.ricker`) was removed in SciPy v1.15, so the original implementation was migrated to the WFDB package.
+
+**Miscellaneous style and typing fixes**
+  Various fixes were made to code style and handling of data types.
+
+
 Version 4.1.2 (June 2023)
 -----------------------------