updated build.sbt to the latest scala (2.10.2) and scalatest (1.9.1)
added solution for Chapter 2 Question 10
for Chapter 3:
fixed solution to Question 1
shorter solution for Question 6
added solution for Question 10
partial solution for Chapter 4:
Chapter 4 (incomplete)
Merge pull request #1 from naory/master

updates for missing solutions