Add a "q" command to the terminal

"q" used to be a unique abbrevation for "quit" before the introduction
of the "quell" command, and it was an easy way to exit terminal mode.

By adding it as an explicit command (must be before all longer
commands starting with "q"), this functionality is regained.

src/term.c

@@ -85,6 +85,7 @@ static int cmd_quell  (PROGRAMMER *pgm, AVRPART *p, int argc, char *argv[]);
 #define _fo(x) offsetof(PROGRAMMER, x)
 
 struct command cmd[] = {
+  { "q",     cmd_quit,  _fo(open),              "abbreviation for 'quit'" },
   { "dump",  cmd_dump,  _fo(read_byte_cached),  "%s <memory> [<addr> <len> | <addr> ... | <addr> | ...]" },
   { "read",  cmd_dump,  _fo(read_byte_cached),  "alias for dump" },
   { "write", cmd_write, _fo(write_byte_cached), "write <memory> <addr> <data>[,] {<data>[,]}" },