Merge pull request #21 from xxdev/develop

Adopting PMML and the new Request format
Merge pull request #23 from xxdev/develop

Code Cleanup
Merge pull request #24 from xxdev/develop

add shifu-plugin-pig and shifu-plugin-dummy
add cleanup for unittest and close output stream for PMML after writing
Merge branch 'develop' of github.com:ShifuML/shifu into develop