Add support for sigils containing integers

[starbelly]

This commit adds support for sigils containing integers. Integers must be proceeded by an upper case alpha, but can otherwise be mixed (e.g., ~A1B2C3).

[starbelly]

Note: I will update sigil docs when a signal this is to be accepted is received :)

[whatyouhide]

I come here with zero context. Was this discussed in the ML or somewhere else?

[starbelly]

I come here with zero context. Was this discussed in the ML or somewhere else?

As is tradition, I give you a context fail 😄 No, this was not discussed on the ML, it simply came up informally on EEF slack. The original context is a potential need to add a sigil that corresponds to a library name that ends with a digit ~HL7.

[whatyouhide]

Gotcha @starbelly no probs, I was just checking. Thanks for the info. 🙏

[starbelly]

@josevalim I think this is good now, but let me know if more adjustments should be made.

[josevalim]

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