Update English documentation.

Update English documentation.
- add description of new configuration directive 'log_destination'
- add description of new configuration directive 'syslog_facility'
- add description of new configuration directive 'syslog_ident'
- add some lines and sample to 'white_function_list' regex usage
- add some lines and sample to 'black_function_list' regex usage
- add information and fix output sample for the 'id' column on
'pool_nodes' command

Patch provided by Gilles Darold.

Also I added description for black_function_list that having lastval
and currval to black_function_list is a good idea.