This function returns a CURLSH handle to be used as input to all the other
share-functions, sometimes referred to as a share handle in some places in the
documentation. This init call MUST have a corresponding call to
curl_share_cleanup when all operations using the share are complete.
This share handle is what you pass to curl using the CURLOPT_SHARE
option with curl_easy_setopt(3), to make that specific curl handle use
the data in this share.
If this function returns NULL, something went wrong (out of memory, etc.)
and therefore the share object was not created.