Minor changes on license comments

Move lincense information into a file

Encoding the license file with UTF-8

Add the license file

Add BSD open source license term

Minor changes for question 44

Rename the project for question 41

Rename a file for question 35

Comment changes for question 23.

Minor changes for question 21.

Add two test cases into question 20.

Minor changes on question 18(2)

Changes on question 26, declaring the type of tree node value as double

Changes for question 14

Changes for backtracking questions.