add notrack support

[Ptival]

This adds support for recognizing and flagging notrack on near jumps and calls.

It makes no attempt at introducing notrack when reassembling.

[RyanGlScott]

It would be worth documenting this new prefix type here:

flexdis86/data/optable.xml

Lines 18 to 23 in ab1ae28

	pfx describes the prefixes that can precede the main opcode without
	turning it into a different instruction. These may be:
	aso - accepts address size override
	oso - accepts operand size override
	rexw, rexr, rexx, rexb - uses the indicated REX bit
	seg - accepts a segment override

Also, I think there is an invariant that notrack cannot be allowed alongside seg, since seg also uses 0x3e (permitting both types of 0x3e would be ambiguous).

[Ptival]

Note: This addresses issue #44