Added enumeration of the three different types of instruction formats,
with a fourth type as a place holder for if the format is unknown.
Initial attempt at defining the instructions.

Currently only the add instruction is defined.
Working towards handling different instructions format based on the mnemonic.

Currently, a skeleton is present in dasm.cpp, and the parser now identifies what
format the add instruction it, but there is much work needed to get it smoother.
Re-thought the instruction definitions.

They now have a constructor such that they can populate a map of mnemonic to
the instruction.