New packaging system (#1810)

+ package.py replaced with invoke <http://www.pyinvoke.org/>
  based tasks.py
  - Run like `invode sdist` or `invode --help`
  - Docstrings missing from tasks!
  - Enhancements like automatically adding version in pom.xml
    and support for deploying sdists.
+ New way to write and read version information.
  - Version stored as one string also with pre-releases (2.8, 2.8b2).
  - Required small changes to code using `get_version()`.
+ Development releases marked with '.devYYYYMMDD' postfix.
  - Compatible with http://legacy.python.org/dev/peps/pep-0440/