Implement probe_lua and add it to lpxclient/lpxserver

luprex/core/cpp/luaconsole.hpp

@@ -18,15 +18,21 @@
 //    /quit               - exit the program
 //    /view               - display the nearby tangibles
 //    /menu [tanid]       - display the menu for tangible 
-//    /snap               - snapshot current state
-//    /roll               - rollback to previous state
 //    /tick [timevalue]   - advance the simulation clock
+//    /choose [number]    - choose menu item number
 //    /1234               - choose menu item 1234
 //
 // If you type anything else, the LuaConsole will generate a
 // syntax error.  Note that not all of the commands above are
 // supported in all interpreters.
 //
+// Lua commands can be one of the following:
+//
+// <expression>       - invoke "<expression>""
+// = <expression>     - invoke "return <expression>"
+// ? <expression>     - probe "<expression>"
+// ?= <expression>    - probe "return <expression>"
+//
 // Once a command has been typed (or a syntax error has been
 // typed), the LuaConsole will return the command.  The command
 // can be fetched using command(), int_arg(), and str_arg()