ruby implementation

This is simple ruby implementation (including snappy compression support).
It is still incomplete (does not have tracking support, refp/refn/alias/object/objectv) and it does have different RB_OBJECT support (it is more like HASH - described in ext/sereal/encode.c, it uses RESERVED + 1 tag).

```
RB_OBJECT tag:  (RESERVED)
class name <STR>
instance variables count <VARINT>
[instance variable name <STR>,instance variable value <ITEM> ,...]
```

```
SRL_HDR_SYM tag: (RESERVED + 1)
len <VARINT>
value - <len> bytes
```

due to the nature of Sereal protocol, it fits very nicely in my work env, and will replace BSON because it is n-times faster (esp. for hashes with few short_binary keys filled with small arrays).
In the future I will implement the cyclic structure.