Add example or function to make it easier to use your own weather data

[birgits]

Weather data in the ModelChain currently needs to be a MultiIndex DataFrame. This has on the one hand the drawback that the data height can only be a scalar and on the other hand that it is not easy to use for people who have not worked with pandas alot.
Concerning the first issue I will wait for the feedinlib weather data class and maybe use ideas from it for the windpowerlib, so either also add a class or use xarray directly.
Concerning the second issue we should provide an example how to create a MultiIndex DataFrame.

[uvchik]

Assuming that weather is a pandas DataFrame with the following column names (pressure, temperature, wind_speed, roughness_length) I solved it the following way:

data_height = {
    'pressure': 0,
    'temperature': 2,
    'wind_speed': 10,
    'roughness_length': 0}
new_columns = [(key, data_height[key]) for key in weather.columns]
weather.columns = pd.MultiIndex.from_tuples(new_columns)

[SabineHaas]

Concerning the first issue I will wait for the feedinlib weather data class [...]

I moved this issue to the v0.1.1 milestone as the feedinlib is not ready, yet.

Concerning the second issue we should provide an example how to create a MultiIndex DataFrame.

This is already done.