Enumeration values should be treated as case-insensitive

[FlorianCassayre]

The Gedcom specification version 5.5.5 page 54 says the following regarding enumerations:

All controlled line_value choices (enumerated values) are case-insensitive. The values "Feb", "FEB" and "feb" are considered equal. A GEDCOM reader must convert all such values to all-uppercase or all-lowercase prior to comparing to internally defined values.

Currently the parser does not make such a distinction and would not properly handle enumeration value that are expressed in lowercase (the date parser partially solves this problem, but not completely).

The proposition is to normalize values to uppercase:

• Locally and systematically when using value parsers
• By calling a special method for simple values, e.g. valueAsEnumeration

[FlorianCassayre]

Turns out what is considered an enumeration appears to be ambiguous: https://www.tamurajones.net/TheGEDCOMDATECase.xhtml

The safest option would be to consider all Value*.ts as enumerations.