vm: use the fmt library to fix shortest decimal representation is…

…sue.

Before:

    IN: scratchpad 0x1.1ffffffffffffp7 .
    144.0

    IN: scratchpad 0x1.2p7 .
    144.0

    IN: scratchpad 0x1.2000000000001p7 .
    144.0

After:

    IN: scratchpad 0x1.1ffffffffffffp7 .
    143.99999999999997

    IN: scratchpad 0x1.2p7 .
    144.0

    IN: scratchpad 0x1.2000000000001p7 .
    144.00000000000003

Perhaps we should implement the Dragonbox algorithm ourselves at some point.

GNUmakefile

@@ -74,6 +74,7 @@ ifdef CONFIG
 		vm/entry_points.o \
 		vm/errors.o \
 		vm/factor.o \
+		vm/format.o \
 		vm/full_collector.o \
 		vm/gc.o \
 		vm/image.o \