Add more options?

[mexn]

Hi,
I was wondering, If you could probably implement options for
a) changing the name/extension of the manifest.json file and
b) tweaking the generated HTML

The reason for this is, that webhint raises errors when the manifest's extension is not .webmanifest (https://webhint.io/docs/user-guide/hints/hint-manifest-file-extension) and the apple-touch-icons have a sizes-attribute resp. appear multiple times (https://webhint.io/docs/user-guide/hints/hint-apple-touch-icons).

[alexander-akait]

PR welcome