api/command for encoding actor params

[magik6k]

Example use:

$ lotus-shed msg encode-params --to f02 --method 4 '"35496873496"'                                                                                                                                                                                                                                                                                                   
RgAIQ8dOGA==

(encode-params-code is similar, but useful when the actor of a given type doesn't exist on-chain (e.g. for serializing constructor params))

[arajasek]

lotus chain encode params does the same thing as the new encode-params

[arajasek]

lgtm