Implement basic netrc parser

I just implemented a `.netrc` parser as I quite often use Python or Curl and have authentication information already in this form. No need to introduce another place to store passwords :grin: 

* A format description may be found at http://linux.die.net/man/5/netrc. 
* I based the implementation for now on the one I found in Python. 
* As I have never used `account` or `macdef` before, I decided to just drop support for these. 
* UTF-8 umlauts and multi-line `.netrc` are supported.

According to [Wikipedia](https://en.wikipedia.org/wiki/Comparison_of_free_and_open-source_software_licenses) the Python license PSF should work fine with Apache 2.0.

This PR includes resp. supersedes #3.