Feature Request: Variable stroke width
Thanks for making Phosphor icons open source, we love them. We really appreciate the attention to detail in retaining a clear consistency of style throughout the set as well as all the thoughtfulness put into their documentation and distribution.

We are currently using Phosphor in our web app at 16px and 20px for most icons, with some 24px and 32px icons for limited cases. We are having a little trouble getting the icon stroke width to look consistent across each size. Even experimenting with the various options (thin, light, regular etc.) we find that the bold 16px icons render a bit thin compared to larger icons of the same style. Additionally, we love the duotone set, but can't use this flexibly as the stroke weight is currently fixed.

We'd like to propose the idea of granular control of stroke width. Of course we recognise it may not be possible to render the icons properly and legibly at all stroke widths, but having some finer control might allow us to get consistency across icon sizes.

Another simpler idea may be to introduce a 'black' weight that helps us beef up icons at smaller sizes. 

Would love to know what you think. If you're on board with this change we're more than happy to submit a pull request.

Thanks again for all your work on this!

Mike and @callum