Move the "show stat" command to stats.c using the CLI keyword API
to register it on the CLI. The stats_dump_stat_to_buffer() function
is now static again.
proto/dumpstats.h has been split in 4 files:
* proto/cli.h contains protypes for the CLI
* proto/stats.h contains prototypes for the stats
* types/cli.h contains definition for the CLI
* types/stats.h contains definition for the stats