release 0.1.16

fixed author reference

fix pointer reference issue

do not test on nightly to avoid marshalling issues

Don't decrease Py_None ref in lastupdate function

Added MANIFEST.in to include header file for source distribution

Rewrote setup script to detect whether newer rrdtool functions can be…

… linked, make fetch callback functions optional to maintain backwards compatibility

Fixed issue #15: C99 is not accepted by some compilers by default

Added package dir to include_dirs in setup.py

Update README.md

Removed Travis CI status image temporarily, as Travis seems to have changed their way how dependency packages are permitted to be used.