Add excluded_search_path_prefixes setting (#1165)

Improves performance in WSL

Fix #1036

* Add excluded_search_path_prefixes setting

Allows filtering the paths used to search for commands
Can be useful to filter out /mnt/ in WSL for performance

* Add test for excluded_search_path_prefixes

* Apply suggestions from code review

Co-authored-by: Pablo Aguiar <scorphus@gmail.com>

Co-authored-by: Pablo Aguiar <scorphus@gmail.com>

tests/test_conf.py

@@ -54,7 +54,8 @@ class TestSettingsFromEnv(object):
                            'THEFUCK_PRIORITY': 'bash=10:lisp=wrong:vim=15',
                            'THEFUCK_WAIT_SLOW_COMMAND': '999',
                            'THEFUCK_SLOW_COMMANDS': 'lein:react-native:./gradlew',
-                           'THEFUCK_NUM_CLOSE_MATCHES': '359'})
+                           'THEFUCK_NUM_CLOSE_MATCHES': '359',
+                           'THEFUCK_EXCLUDED_SEARCH_PATH_PREFIXES': '/media/:/mnt/'})
         settings.init()
         assert settings.rules == ['bash', 'lisp']
         assert settings.exclude_rules == ['git', 'vim']
@@ -65,6 +66,7 @@ class TestSettingsFromEnv(object):
         assert settings.wait_slow_command == 999
         assert settings.slow_commands == ['lein', 'react-native', './gradlew']
         assert settings.num_close_matches == 359
+        assert settings.excluded_search_path_prefixes == ['/media/', '/mnt/']
 
     def test_from_env_with_DEFAULT(self, os_environ, settings):
         os_environ.update({'THEFUCK_RULES': 'DEFAULT_RULES:bash:lisp'})