FIX: Performance measuring statistics

On Linux systems SystemTap infrastructure can be used
to gather information of a running system. This patch
adds probes to a few places withing libtrading FIX
engine. A few examples show how to assess FIX engine
performance. In particular, we calculate the precise
amount of time spent on parsing messages and time spent
on sending or receiving data through the net.

The interface used can be extended to the systems with
other than SystemTap infrastructure e.g. dtrace. Probes
can also be switched off if there is no way to use any
technique of the above.

By default probes are switched off.

Usage example:

 $ sudo stap -c "./tools/fix/fix_client -m order -n 1000 -h localhost -p 9000" ./tools/fix/fix_client.stp -o out.txt
 $ cat out.txt | awk -f './tools/fix/fix_client.awk'
 fix_message_unparse_time_ret:      13479
 fix_message_unparse_ret:            1002
 fix_message_unparse_time_err:          0
 fix_message_unparse_err:               0
 fix_message_parse_time_ret:         8646
 fix_message_parse_ret:              1002
 fix_message_parse_time_err:         2292
 fix_message_parse_err:              1092
 fix_message_recv_time_ret:        102910
 fix_message_recv_ret:               1002
 fix_message_recv_time_err:          4111
 fix_message_recv_err:                 45
 fix_message_send_time_ret:         52249
 fix_message_send_ret:               1002
 fix_message_send_time_err:             0
 fix_message_send_err:                  0

Signed-off-by: Marat Stanichenko <mstanichenko@gmail.com>
Signed-off-by: Pekka Enberg <penberg@iki.fi>