Analog devices , power, current sources added, Examples for registers added and some minor bugs fixed

* Examples for Register, Shift Register, Circular shift register added
* Class name changed from ````FourBitRegister2```` to ````FourBitLoadRegister```` 
* bugs in ````setOutput```` fixed
* Bug #175 corrected
* Analog device ````Resistor```` class added
* Analog sources ````Source```` , ````Current Source````, ````Voltage Source````, etc added.
* Bug #178 corrected
* ````IC_4030```` added