decoder skeleton code: this should be able to read any MIPS instruction and decode...

decoder skeleton code: this should be able to read any MIPS instruction and decode it but NOT produce any C++ class object.
All of the code literals are empty as of now. As much as possible instructions were organized into relevant "formats"
and also references to the tables I used from the MIPS manual were noted via appropriate comments.

--HG--
extra : convert_revision : 9b44fb40e900061a4cdb290b6a5aaceb9750ae13