Replace BER encoding with MsgPack everywhere

This commit completely changes the data format used by Tarantool.
A new binary serialization format called MsgPack (http://msgpack.org)
has been introduced to store tuples, keys, request members, etc.
MsgPack supports various data types and hierarchical structures. Since
tuple & keys format has been changed, the binary protocol is no more
compatible with 1.5 clients.

The list of major changes:

 * Add MsgPack library and unit tests as a submodule
 * Add Lua bindings for the library and unit tests for it
 * Update IPROTO to use MsgPack for all kinds of requests
 * Change struct tuple to use MsgPack Array instead of BER-encoded fields
 * Remove fixed offsets from tuples (cannot be supported by MsgPack)
 * Replace const char *key, key_part pairs with MsgPack Arrays
 * Rework comparators and indicies to support MsgPack'ed fields
 * Merge NUM and NUM64 types into the one single type (NUM)
 * Rewrite box_lua.cc functions to support MsgPack instead of BER
 * Rewrite tuple_update to support MsgPack instead of BER
 * Totaly remove varint32 functions from all modules
 * Rework lua_tofield and YAML encoder to properly support Lua tables
 * Modifie bootstrap files and system spaces to use the new format
 * Add MsgPack support to the test system via msgpack-python
 * Update tests to use proper data types and remove unneeded box.packs

Tarantool 1.6 is the world's first MsgPack-based database!