Upgrade pyowm to 2.7.1

[fabaff]

2.7.1

New features:

• introduced support for Sulphur Dioxide (SO2) and Nitric Dioxide (NO2): new methods owm25.no2index_around_coords and owm25.so2index_around_coords
• implemented wind speed units specification (imperial/metric)

Bugfixes:

• updated weather history endpoint (was broken)
• fix bug about data parsing at station_at_coords and weather_at_station methods
• now the deg attribute is correctly parsed from 16 day forecast weather data items
• fix bug on printing Unicode upon library exceptions
• fix handling of Weather objects parsing (it was failing whenever some data wasn't provided by OWM)

Enhancements:

• shrinked city ID files size by 60% (via compression)
• reported in the Wiki a list of known projects that use PyOWM
• integrated the Say Thanks! hook
• introduced CONTRIBUTING.md and CODE_OF_CONDUCT.md files, thus welcoming GitHub's suggested best practices for building better open source communities
• introduced installation tests
• improved integrations tests organization and running

Breaking changes:

OWM decided to change the syntax of API endpoint for fetching UV data and its format in a non-retrocompatible manner. This results into UVIndex object entity fields changing, as well as the corresponding OWM25 method signature (owm25.uvindex_around_coords).

Related issue (if applicable): fixes #7512

Tested with the following configuration:

sensor:
  - platform: openweathermap
    api_key: !secret owm_api
    forecast: 0
    monitored_conditions:
      - weather
      - temperature
      - wind_speed
      - humidity
      - pressure
weather:
  - platform: openweathermap
    api_key: !secret owm_api

[mention-bot]

@fabaff, thanks for your PR! By analyzing the history of the files in this pull request, we identified @balloob, @rmkraus and @robbiet480 to be potential reviewers.