as TS_RESP_CTX is not thread safe, this commit implement a pool of
TS_RESP_CTX in which a thread can pick one in a thread safe maner.
* implement a ts_resp_ctx_wrapper containing a TS_RESP_CTX and a
lock and bool to mark the availability of the TS_RESP_CTX
* implement the get_ctxw to recover a given TS_RESP_CTX in a thread safe
maner
* adapt the rest of the code to accomodate the new way of doing things
* set the default number of threads to 10 as it's now safe to do so
* pass the size of the query to the create_response function
* implement a serial generator based on random numbers
* fix the creation of the bio for the query content
* add logging for the create_reponse
TODO:
* some REAL memory cleaning...
* split the rfc3161 and the http part
* add a logger function
* add a debugging logger function for the requests
* add a specific handler for rfc3161 request
