Pycurl

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* Add CURLOPT_MAXLIFETIME_CONN (patch by fsbs).

* Easy handle duplication support (patch by fsbs).

* Support for unsetting a number of multi options (patch by fsbs).

* pycurl classes can now be subclassed (patch by fsbs).

* Multi callbacks' thread state management fixed (patch by fsbs).

* Add CURL_LOCK_DATA_PSL (patch by fsbs).

* Add support for SecureTransport SSL backend (MacOS)
(patch by Scott Talbert).

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* Fixed Python thread initialization causing hangs on operations
(patch by Scott Talbert).

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* getinfo(CURLINFO_FTP_ENTRY_PATH) now handles NULL return from
libcurl, returning None in this case.

* Python 3.9 is now officially supported (patch by Bill Collins).

* Added CURLOPT_DOH_URL (patch by resokou).

* Best effort Python 2 support has been reinstated.

* Added missing fields to curl_version_info struct (patch by Hasan).

* Added CURLINFO_CONDITION_UNMET (patch by Dima Tisnek).

* Exposed MAX_CONCURRENT_STREAMS in CurlMulti (patch by Alexandre Pion).

* Compilation fixed against Python 3.10 alpha (patch by Kamil Dudka).

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* Fixed offset parameter usage in seek callback (patch by Scott Talbert).

* Added support for libcurl SSL backend detection via
`curl-config --ssl-backends` (patch by Scott Talbert).

* Added support for libcurl MultiSSL (patch by Bo Anderson).

* Added ability to unset CURLOPT_PROXY.

* Added support for CURLOPT_UPLOAD_BUFFERSIZE (patch by Artur Sobierak).

* Added support for CURLOPT_MAXAGE_CONN (patch by Artur Sobierak).

* Added support for sharing connection cache in libcurl (patch by
Artur Sobierak).

* Added support for CURLOPT_HAPROXYPROTOCOL (patch by
Russell McConnachie).

* CC and CFLAGS environment variables are now respected when building
(patch by Michał Górny).

* Fixed OpenSSL detection on CentOS 7 and 8 (patch by Nicolas Pauss).

* surrogateescape error handler is used in multi_info_read to handle
invalid UTF-8.

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* Fixed build with recent Pythons on RHEL/CentOS.

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* Minimum supported Python 3 version is now 3.5.

* Python 2 is no longer officially supported.

* Improved thread safety of multi code.

* Added Python 3.8 support (patch by Michael Treanor).

* Fixed link order when linking statically against OpenSSL (patch by
Ashley Whetter).

* Fixed Darwin detection.

* Added support for wolfSSL (patch by Eneas U de Queiroz).

* Added PROXY_SSL_VERIFYHOST (patch by Amir Rossert).