Added javascript deck code encoder and parser#10

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NorthFury wants to merge 3 commits intoValveSoftware:masterfrom

NorthFury:javascript

Commits on Nov 11, 2018

added javascript decoder
NorthFury
committed

Commits on Nov 12, 2018

added javascript encoder
NorthFury
committed

Commits on Nov 13, 2018

use zero fill right shift to avoid potential errors
NorthFury
committed