This function must be the first function to call, and it returns a CURL easy
handle that you must use as input to other easy-functions. curl_easy_init
initializes curl and this call MUST have a corresponding call to
curl_easy_cleanup(3) when the operation is complete.
If you did not already call curl_global_init(3),
curl_easy_init(3) does it automatically.
This may be lethal in multi-threaded cases, since curl_global_init(3) is
not thread-safe, and it may result in resource problems because there is
no corresponding cleanup.
You are strongly advised to not allow this automatic behaviour, by
calling curl_global_init(3) yourself properly.
See the description in libcurl(3) of global environment
requirements for details of how to use this function.
If this function returns NULL, something went wrong and you cannot use the
other curl functions.