MEDIUM: sample: add the "map" converter

MEDIUM: sample: add the "map" converter

Add a new converter with the following prototype :

  map(<map_file>[,<default_value>])
  map_<match_type>(<map_file>[,<default_value>])
  map_<match_type>_<output_type>(<map_file>[,<default_value>])

It searches the for input value from <map_file> using the <match_type>
matching method, and return the associated value converted to the type
<output_type>. If the input value cannot be found in the <map_file>,
the converter returns the <default_value>. If the <default_value> is
not set, the converter fails and acts as if no input value could be
fetched. If the <match_type> is not set, it defaults to "str".
Likewise, if the <output_type> is not set, it defaults to "str". For
convenience, the "map" keyword is an alias for "map_str" and maps a
string to another string. The following array contains contains the
list of all the map* converters.

                 +----+----------+---------+-------------+------------+
                 |     `-_   out |         |             |            |
                 | input  `-_    |   str   |     int     |     ip     |
                 | / match   `-_ |         |             |            |
                 +---------------+---------+-------------+------------+
                 | str   / str   | map_str | map_str_int | map_str_ip |
                 | str   / sub   | map_sub | map_sub_int | map_sub_ip |
                 | str   / dir   | map_dir | map_dir_int | map_dir_ip |
                 | str   / dom   | map_dom | map_dom_int | map_dom_ip |
                 | str   / end   | map_end | map_end_int | map_end_ip |
                 | str   / reg   | map_reg | map_reg_int | map_reg_ip |
                 | int   / int   | map_int | map_int_int | map_int_ip |
                 | ip    / ip    | map_ip  | map_ip_int  | map_ip_ip  |
                 +---------------+---------+-------------+------------+

The names are intentionally chosen to reflect the same match methods
as ACLs use.