We can make the implementation more robust by adjusting our assumptions
and leverage explicit file modes for syncing. Additionally we going to
assume that we want to clean up and can't really recover if thos
operations (file close and removal) fail.
* utilise file mode for majority of concerns
* improve test coverage by covering more assumptions
* signature parity with ioutil.WriteFile
* always clean up
Replaces #160
Alexander Simmerl
Anton Kaliaev