Add iotools functions for Meteonorm

[AdamRJensen]

• I am familiar with the contributing guidelines
• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

This PR adds functions for retrieving irradiance and weather data from Meteonorm. This is the last function I plan on contributing to the commercial iotools, as pvlib then will support what I consider the major providers of satellite-derived irradiance data.

Documentation:

• get_meteonorm
• get_meteonorm_tmy

For anyone willing to review this PR, I can provide a temporary API key.

[IoannisSifnaios]

Some minor things here and there. Otherwise LGTM!