main ins no longer needed in command

- MAIN is automatically replaced by the basename of the home directory
- when %(ins) is omitted in *_command, it is also replaced by this
+ add help subcommand

base.py

@@ -83,6 +83,7 @@ class ServiceManager:
     pkg = ''
     revcmd = {}
     USAGE = None
+    main_instrument = basename(expanduser('~'))
 
     def __init__(self):
         self.env = {}
@@ -136,7 +137,7 @@ class ServiceManager:
         for ins in parser.sections():
             section = dict(parser[ins])
             if ins == 'MAIN':
-                ins = basename(expanduser('~'))
+                ins = self.main_instrument
             command = section.get('%s_command' % self.group)
             self.revcmd[command] = self.group
             nr = section.get(self.group)
@@ -192,7 +193,7 @@ class ServiceManager:
                     match = cmdpat.match(cmd)
                     if match:
                         gdict = match.groupdict()
-                        ins = gdict['ins']
+                        ins = gdict.get('ins', self.main_instrument)
                         serv = gdict.get('serv', '')
                         if cfginfo is not None and 'cfg' in gdict:
                             cfginfo[ins, serv] = gdict['cfg']