adds support for Health Icons

[tomjemmett]

Resolves #73 by adding support for the Health Icons set. This adds the function download_health_icons() and the icon set health_icons.

Health Icons provide a single download file which is the most recent set of icons. It does not appear as though they have an archive for previous versions, so there is no version argument to download_health_icons

It appears as though this is most similar to Google material for the way to search for icons, so I have copied that pattern. The following work:

• health_icons("blood_bag")
• health_icons("blood_bag", theme = "negative")
• health_icons("blood_bag", category = "blood", theme = "negative")

however, providing a category but no theme fails

• health_icons("blood_bag", category = "blood")

Does this feel like it's in keeping with the rest of the package? Happy to make any changes necessary.

[Moohan]

I did a quick check of this, using it in a Shiny app and it seemed to work as expected!

[mitchelloharawild]

Looks great, thanks for your contribution!
If you'd like, could you please add yourself to the DESCRIPTOIN as a ctb author?

Thanks also for figuring out how to extend the package despite no extension documentation being written yet. Well done! 🎉

[tomjemmett]

added myself to DESCRIPTION! 🙂

[mitchelloharawild]

Looks good, thanks for your PR!