update preface.md
update
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
add chapter04 part, to be continue, update cpp Makefile
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Chapter1 java code
Merge remote-tracking branch 'upstream/master'
Merge pull request #128 from RONGHAI/master

ruby version for chapter 02 & 03
improve chapter 27 readability
fix chapter 27 hyperlink
Update about in Readme.md
Add reference for binary_search from Peter Norvig
java code for chapter1 & 2
Merge branch 'master' of https://github.com/schemacs/The-Art-Of-Programming-By-July
adding java code for chapter1 & 2