Implement fmt_human_2() and fmt_human_10()

These functions take the raw number and a unit and automatically
print it out "scaled down" to a proper SI-prefix, for powers of 2
and 10 respectively.

Apply them to the 2-power cases and keep the 10-power for a later
commit.

components/disk.c

@@ -16,7 +16,7 @@ disk_free(const char *mnt)
 		return NULL;
 	}
 
-	return fmt_scaled(fs.f_frsize * fs.f_bavail);
+	return fmt_human_2(fs.f_frsize * fs.f_bavail, "B");
 }
 
 const char *
@@ -43,7 +43,7 @@ disk_total(const char *mnt)
 		return NULL;
 	}
 
-	return fmt_scaled(fs.f_frsize * fs.f_blocks);
+	return fmt_human_2(fs.f_frsize * fs.f_blocks, "B");
 }
 
 const char *
@@ -56,5 +56,5 @@ disk_used(const char *mnt)
 		return NULL;
 	}
 
-	return fmt_scaled(fs.f_frsize * (fs.f_blocks - fs.f_bfree));
+	return fmt_human_2(fs.f_frsize * (fs.f_blocks - fs.f_bfree), "B");
 }