add think python

think pythonとはAllen Downey氏が書いているthinkシリーズの１つである．
他のThinkシリーズは[こちら](http://greenteapress.com/)からご覧になれます．
Merge branch 'master' of https://github.com/vhf/free-programming-books
Merge pull request #946 from SamuraiT/master

add thnk python
Move Awk book from Unix section to Awk section.
Awk book -> Awk section (from Unix)

Move Awk book from Unix section to Awk section and remove typo extra line.
Merge pull request #951 from hoganlong/master

Move Awk book from Unix section to Awk section.