Chainspec with Metadata

[mkchungs]

Following the suggestions from #24, Chanspec has now been enhanced with StructType & Metadata:

type KeyVal struct {
	Key        []byte `json:"k"`
	Value      []byte `json:"v"`
	StructType string `json:"struct_type,omitempty"`
	Metadata   string `json:"meta,omitempty"`
}

Example:

...
		[
            "0x01fe00ff00ff00ff930bed80bb11dd6dfd43b1655fd441595bd019b66960192f",
            "0x00000000000000000020006200000000005428110000002810000000281c000000284133073200140a0400fffe00000000330b08330732009511f87b1014080000fffe000000008087808804140a00e0fdfe000000003309640a0b821095110832003307320021842a80540aa004904a05",
            "account_preimage",
            "s=1|h=0x74930bed80bb11dd6dfd43b1655fd441595bd019b66960192f9964f61eceee84|plen=113"
        ]
...

        [
            "0xff01000000000000000000000000000000000000000000000000000000000000",
            "0x74930bed80bb11dd6dfd43b1655fd441595bd019b66960192f9964f61eceee84a08601000000000064000000000000006400000000000000c20000000000000002000000",
            "service_account",
            "s=1|b=100000 g=100 m=100 l=194 i=2|clen=32"
        ]

This shall provide all information needed for decoding of the structs. Noted that:
(1) key is 32 bytes (not 31 bytes).
(2) If (1) is true, then running state transition does not require any knowledges of non c1-c15 keys {a_s, a_p, a_l} -- as long as other clients can start with same state root and list of [{k,v}]