2nd parsing pass

Two parsing passes now exist. The new one, the latter, parses the operands
a bit better. It can handle all three different operand types (immediate,
register, memory). As before, all data is now stored in enums, and lookup
tables are used in parsing.

Memory addressing modes are also parsed now, all the 17 modes have their
own enum value, and in addition the possible displacement is stored too
(set to 0 as default). Segment overriding is still undone.