================================================================================
Array#pack
================================================================================
+-----------+------------------------------------------------------------------+
| Directive | Meang |
+-----------+------------------------------------------------------------------+
| @ | Moves to absolute position |
| A | ASCII string (space padded, count is width) |
| a | ASCII string (null padded, count is width) |
| B | Bit string (descending bit order) |
| b | Bit string (ascending bit order) |
| C | Unsigned char |
| c | Char |
| D, d | Double-precision float, native format |
| E | Double-precision float, little-endian byte order |
| e | Single-precision float, little-endian byte order |
| F, f | Single-precision float, native format |
| G | Double-precision float, network (big-endian) byte order |
| g | Single-precision float, network (big-endian) byte order |
| H | Hex string (high nibble first) |
| h | Hex string (low nibble first) |
| I | Unsigned integer |
| i | Integer |
| L | Unsigned long |
| l | Long |
| M | Quoted printable, MIME encoding (see RFC2045) |
| m | Base64 encoded string |
| N | Long, network (big-endian) byte order |
| n | Short, network (big-endian) byte-order |
| P | Pointer to a structure (fixed-length string) |
| p | Pointer to a null-terminated string |
| Q, q | 64-bit number |
| S | Unsigned short |
| s | Short |
| U | UTF-8 |
| u | UU-encoded string |
| V | Long, little-endian byte order |
| v | Short, little-endian byte order |
| w | BER-compressed integer\fnm |
| X | Back up a byte |
| x | Null byte |
| Z | Same as ``a'', except that null is added with * |
+-----------+------------------------------------------------------------------+
