Implement file(1).

Unlike the POSIX file(1), there's no magic file here, just hard-coded
common (non-obsolete) file formats. Personally most of my use of file(1)
is as a one-line readelf(1) summarizer, so although I assume a full POSIX
file(1) is out of scope (because just the database would likely be larger
than all the rest of toybox), a subset that only supports in-use file types
actually covers most of the use cases I encounter personally.

Also fix peek_be/peek_le.
diff --git a/lib/lib.c b/lib/lib.c
index 681d4d2..e80b8b1 100644
--- a/lib/lib.c
+++ b/lib/lib.c
@@ -508,8 +508,7 @@
   char *c = ptr;
   int i;
 
-  for (i=0; i<size; i++) ret |= ((int64_t)c[i])<<i;
-
+  for (i=0; i<size; i++) ret |= ((int64_t)c[i])<<(i*8);
   return ret;
 }
 
@@ -517,9 +516,9 @@
 {
   int64_t ret = 0;
   char *c = ptr;
+  int i;
 
-  while (size--) ret = (ret<<8)|c[size];
-
+  for (i=0; i<size; i++) ret = (ret<<8)|(c[i]&0xff);
   return ret;
 }