add chapter 30~31
Update 30.0~31.0.md
Update 30.0~31.0.md
Update 30.0~31.0.md
Update preface.md
Merge remote-tracking branch 'upstream/master'
update
Update preface.md
update
update
remove preface.md.bak
Delete .directory
update
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
add chapter 38
Update 02.0.md

之前的bit hack有误，0x3f需要改为0x1f。同时考虑到bit version容易误导人，可读性也不强。所以加入了histogram version。
Merge pull request #83 from blackball/patch-1

Update 02.0.md
Merge pull request #82 from badnotes/master

add chapter 38
Update preface.md