Search matching style

The MODULES_SEARCH_MATCH environment variable is introduced to define the matching style to perform when searching for available modules. With starts_with value, modules whose name begins by search query string are returned. When search match style is set to contains, modules returned are those whose fully qualified name contains search query string.

Configure option --with-search-match defines this setting which can be superseded by the environment variable. This environment variable can be set with the config module sub-command via the search_match option. All these configuration means can be superseded in turns by the --starts-with/-S and --contains/-C command-line switches of the avail module sub-command.

$ module avail oo
$ module avail -C oo
----------- /path/to/modulefiles ------------
foo/1 foo/2
$ module config search_match contains
$ module avail oo
----------- /path/to/modulefiles ------------
foo/1 foo/2