This function must be the last function to call for an easy session. It is the
opposite of the curl_easy_init(3) function and must be called with the
same handle as input that the curl_easy_init call returned.
This will effectively close all connections this handle has used and possibly
has kept open until now. Don't call this function if you intend to transfer
Any uses of the handle after this function has been called are
illegal. This kills the handle and all memory associated with it!
With libcurl versions prior to 7.17.: when you've called this, you can safely
remove all the strings you've previously told libcurl to use, as it won't use
them anymore now.