add CHANGELOG.md for v0.1.0

Document notable changes in the project, including added features, changes, and fixes.

Author: laxmena

CHANGELOG.md

@@ -0,0 +1,28 @@
+# Changelog
+
+All notable changes to PyCalendly will be documented here.
+
+## [0.1.0] - 2026-03-27
+
+### Added
+- OAuth2 authentication support via new `CalendlyOauth2` class
+- `get_access_token` — exchange authorization code for access token
+- `revoke_access_token` — revoke a given access token
+- `refresh_access_token` — refresh an existing access token
+- `introspect_access_token` — retrieve details about a token
+- `authorization_url` property for building the OAuth2 authorization URL
+- Dedicated `CalendlyException` and `CalendlyOauth2Exception` exception classes in `exceptions.py`
+
+### Changed
+- **Breaking:** `CalendlyReq.process_request` now raises `CalendlyException` on HTTP 4xx/5xx responses instead of returning the raw response
+- Renamed internal `utils/requests.py` to `utils/api.py` to avoid shadowing the `requests` package
+- Mutable default argument in `create_webhook` changed from `list` to `tuple`
+- Return type annotations corrected on `list_event_types`, `list_events`, `get_all_event_types`, `get_all_scheduled_events`
+
+### Fixed
+- Removed unnecessary parentheses in conditionals throughout `calendly.py`
+- `user == None` replaced with `user is None`
+
+## [0.0.1] - 2021-07-29
+
+- Initial release