* add a DL button + serve the signer certificate file (the one used to
timestamp)
* fix the verification instruction (add -untrusted tsa_cert.pem)
* few CSS tweaks to improve page layout
* disable stdout buffering when logging to stdout
* add 'log_to_syslog' parameter in configuration file to enable/disable
logging to syslog
* add 'log_to_stdout' parameter in configuration file to enable/disable
logging to stdout
slight clean-up and reformatting also (thanks to clang-format new
version)
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