Instantiate TimeSeries from a csv file

[misi9170]

WindRose and WindTIRose have capabilities of reading data from CSVs using their own (static) read_csv_long() methods. However, the TimeSeries class, until now, has not supported such functionality. This PR adds a new static method read_csv() to the TimeSeries class to enable such functionality.

To be discussed:

• The new TimeSeries.read_csv() allows users to specify a value_col, whereas WindRose.read_csv_long() and WindTIRose.read_csv_long() do not support reading in a value_col. Do we want to add this optional keyword arguments to WindRose.read_csv_long() and WindTIRose.read_csv_long()?
• I chose to use TimeSeries.read_csv() rather than TimeSeries.read_csv_long() because I think the "long" format is implied by the "series" nature of the class. However, we could use read_csv_long instead to match the other wind data classes.
• None of the WindData classes have a to_csv() method, but this also seems like a natural counterpart. We could consider adding one for TimeSeries and possibly also WindRose and WindTIRose

Tagging @paulf81 , @ejsimley in case they have thoughts on this.

[paulf81]

• The new TimeSeries.read_csv() allows users to specify a value_col, whereas WindRose.read_csv_long() and WindTIRose.read_csv_long() do not support reading in a value_col. Do we want to add this optional keyword arguments to WindRose.read_csv_long() and WindTIRose.read_csv_long()?

Sure, does seem reasonable!

• I chose to use TimeSeries.read_csv() rather than TimeSeries.read_csv_long() because I think the "long" format is implied by the "series" nature of the class. However, we could use read_csv_long instead to match the other wind data classes.

TimeSeries.read_csv() does make sense would always be long. Could alias TimeSeries.read_csv_long() for completeness? Or maybe the more perfect is the function is defined in TimeSeries.read_csv_long() and TimeSeries.read_csv() is its alias?

• None of the WindData classes have a to_csv() method, but this also seems like a natural counterpart. We could consider adding one for TimeSeries and possibly also WindRose and WindTIRose

I could see it. In FLASC I do sometimes call up FLORIS just for the WindRose classes and a work flow of loading a TimeSeries object, converting to WindRose and then exporting the WindRose to csv could have a place.