add solution to Problem 3 in Problem Set 1.

Augmented are the following 2 files:

	DigitsToStringConverter.java
	DigitsToStringConverterTest.java

Thank you!
							Lawrence X. Amlord
							  Oct 4th, 2014
							  Xi'an, China
add solution to Problem 4 in Problem Set 1.

Augmented are the following 2 files:

	WordFinder.java
	WordFinderTest.java

Thank you!
							Lawrence X. Amlord
							  Oct 4th, 2014
							  Xi'an, China