Release v2.17.1

Changes in v2.17.1

• fixed in windrose.py: Sectors started at 0° and are not centred on north. ring drew its lines on the sector borders instead of the sector centres. The season labels were misspelled. The seasons were off by one month windrose_histogram failed if no 'KM' column is present
• exposed plot_windrose as external function for programmatic use in windrose.py