Doesn't handle short codes properly

[johns10]

This library doesn't appear to handle short codes properly.

Check this case:

iex(1)> {:ok, phone_number} = ExPhoneNumber.parse("88811", "US")        
{:ok,
 %ExPhoneNumber.Model.PhoneNumber{
   country_code: 1,
   national_number: 88811,
   extension: nil,
   italian_leading_zero: nil,
   number_of_leading_zeros: nil,
   raw_input: nil,
   country_code_source: nil,
   preferred_domestic_carrier_code: nil
 }}
iex(2)> ExPhoneNumber.is_valid_number?(phone_number)
false

That is a valid shortcode, from which I received a confirmation code.

I'd be willing to take this on. A little guidance on where to read the code to port from in libphonenumber, and where it should go in ex_phone_number would be super helpful.

[johns10]

My first question here is:

Should the PhoneNumber struct land with a country code?

It seems like a significant portion of this library leans on having a country code.

https://en.wikipedia.org/wiki/Short_code#:~:text=the%20shortcode%20number.-,United%20States,Short%20Code%20Administration%20and%20CTIA.

However, in terms of dialing, they don't appear to be used. So, I'm not sure what the right choice is here.

[johns10]

Ah, we don't have to define this, do we?

Apparently there is a short code standard defined alongside PhoneNumberMetaData.xml

https://github.com/google/libphonenumber/blob/master/resources/ShortNumberMetadata.xml

[johns10]

I was initially looking at creating new metadata for this, but the more I look, there is a pretty standard format, and we can probably just lean on the PhoneNumberDescription in ShortNumberMetadata.xml

[johns10]

I took a stab at this by fetching the ShortNumberMetadata and naively merging it in to the metadata struct. This broke 89 tests right off the bat, so maybe not the best approach?

[johns10]

I made a PR for this. Its in no way complete or clean. I wanted to share what I've done so far for feedback. This is a bit of a yak shave for me so I implemented short code validation before creating phone numbers. Ya'll let me know what you think.

#71