Addition of RegH and RegL classes

This improves the registers interface, so every registers, even the most
and less significant ones may be accessed by 'value' attribute.

Another few change is renaming of class Reg => Reg16
Registers class improving of get/set item
BaseReg class

This class is to be inherited by all classes that represent registers.

Additionally a StructReg class which inherits BaseReg is available to
allow use of ctypes.Structure resources.
Improving Registers class
Cycle working for MOV, NOP and HALT
Renaming: CPUCycle => MachineCycle
Joined InstructionWord and DataWord into Word class

Now just has one Word class that works in the same way to DataWord
perspective but not for InstructionWord.

In this later, now it's needed to pass is_instruction arg as True, so

    InstructionWord(1, 2, 3, lineno=6)

now becomes

    Word(1, 2, 3, lineno=6, is_instruction=True)