remove useless count_args of Msg...
Parameter of count_if in count_args of ArgParser, Use constness and reference to remove pass by value copy.
prettify Msg.h, remove tailing spaces, expand if-else
rename left_pos to submsg_begin, and right_pos to submsg_end
rename src to src_msg, rename result to dst_msg
compact the dst_msg creation
extract value management in Msg.h to a class ArgValue