Carsons

Carsons now supports adding a `frequency` attribute to line models, allowing support for modelling line impedance in circuits operating at frequencies other than 60hz.

This bug-fix addresses 27, where it was found that on systems that did not have a default encoding of `UTF-8` python was opening the readme file during installation and then failing when it encountered unicode characters. By opening the readme with a specified encoding of `UTF-8`, we can ensure that `carsons` will install on any system that supports this encoding.

Converts the README to markdown, so it will render properly on [pypi](https://pypi.org/project/carsons/)

carsons` now supports modelling of concentric neutral cable with any phasings.

Previously, Carsons required a line model that provided a map describing the phases, with the keys matching how data was available for gmr, resistance and position.

With this update, you no longer need to provide a map -- an iterable of the phases will suffice.

python

line.phases = {'A', 'B', 'C'}


Of course, the map version is still supported, and may continue to be useful if you have custom objects that you want to look up by phase in order to build your model.

Adds a readme describing in basic terms what `carsons` is and does