parse inline string values

[kenichi]

• set value_type to :inline_string on tag start
• capture cdata value when :inline_string
• test for values in existing test file

[kenichi]

slightly different than #108 which I probably would've just used if i'd looked first 😂

[RodolfoSilva]

@jsonkenl could you merge this fix?

[RodolfoSilva]

Here the spec:

https://learn.microsoft.com/en-us/dotnet/api/documentformat.openxml.spreadsheet.inlinestring?view=openxml-2.8.1#remarks

[jsonkenl]

@kenichi Please resolve conflicts and I'll get this merged.

[kenichi]

@RodolfoSilva thanks for the suggestions, @jsonkenl resolution incoming...