Add and demonstrate example ini file

mkit.ini

 
 [files:share]
     src/shellfu/saturnin.sh     = shellfu/saturnin.sh
+    src/ini.d/main/echo.ini     = ini.d/main/echo.ini

src/ini.d/main/echo.ini

+
+[echo]
+
+    #
+    # default prefix
+    #
+    prefix = so:

src/libexec/satcmd-echo

 #!/bin/bash
 
+. "$(shellfu-get path)" || exit 3
+
+shellfu import inigrep
+
+SATCMD_ECHO__PREFIX="${SATCMD_ECHO__PREFIX:-$(inigrep -p "echo.prefix")}"
+
+echo -n "$SATCMD_ECHO__PREFIX"
 echo "$@"