Merge pull request #4 from yunfuliu/master

v0.2.0
Merge pull request #10 from yunfuliu/master

merge for v0.3.0
Merge pull request #14 from yunfuliu/master

pixkit0.4.0
Merge pull request #27 from yunfuliu/master

pixkit v0.5.0
Merge pull request #32 from yunfuliu/master

pixkit v0.5.1
Merge branch 'master' of https://github.com/yunfuliu/pixkit into release
Merge branch 'master' of https://github.com/yunfuliu/pixkit into release
peer group filitering

add new method
bug fix
bug fix pgf
fix problem
fix file name
Merge pull request #48 from jerrycoolwu/release

peer group filtering