language-coverage-details: Support temp char lists

[davelab6]

• I'd like to be able to input new (temporary) character sets from a textarea input (plus label input etc) as sometimes I get a list of characters and I want to know quickly if the font supports those characters.

I'm guessing the simplest thing is to have an input that accepts unicode characters as themselves; and to set the new temp set with a label, and then 1+ textareas for the lax list, the strict list...

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Bonus ideas would be

• to support inputs in the variety of typical ways lists of unicode points are kept (eg https://r12a.github.io/apps/conversion)
• to load the input from a URL
• to cache/store the lists on localStorage, and
• to load/save the lists from Github (using the Github API as http://prose.io does)

but those are not really needed :)