Wrong decoding of negative numbers and no support for boolean and null values

[bialix]

This is CBOR byte stream I've used to test different types and values. I found problems with negative integer values < -16 and also not supported types boolean and null. For the latters there is awaiting pull request.

B4 63 70 31 36 10 63 75 6E 69 76 E9 80 9A E8 A8
8A E9 80 A3 E6 8E A5 E5 9F A0 20 28 43 4F 4D 31
29 62 6E 31 20 65 61 73 63 69 69 65 68 65 6C 6C
6F 63 6E 69 6C F6 69 65 6D 70 74 79 5F 61 72 72
80 66 70 36 35 35 33 35 19 FF FF 63 62 69 6E 43
31 32 55 63 6E 32 47 3A 7F FF FF FF 62 70 31 01
66 6E 36 35 35 33 35 39 FF FE 63 6E 31 36 2F 64
7A 65 72 6F 00 63 61 72 72 83 01 02 03 63 6F 62
6A A1 63 66 6F 6F 63 62 61 72 66 62 66 61 6C 73
65 F4 64 70 32 35 35 18 FF 63 70 32 47 1A 80 00
00 00 64 6E 32 35 35 38 FE 65 62 74 72 75 65 F5

It's easy to test what should be decoded on site http://cbor.me/