add function of using javapoet to generate java files

[tomridder]

add function of using javapoet to generate java files #554

benifits:

1. it is type safe, making it easier to refactor with.
2. it is more safe because it will add import automaticly
3. make code more elegent and easy to read by the thought of OOP 1.txt 2.txt the files are the code generated by javapoet and Bufferwriter I check the content they were same the all the test cases in TestModule has been passed :)

[greenrobot-team]

Thanks for submitting! We'll consider this for an upcoming release.

[tomridder]

my pleasure :)

by the way ,what ' the date of next upcoming release