Add more 7.0 sample files

[dthaler]

Copy 8 files from https://github.com/gedcom7code/test-files/tree/main/7 that exercise parts of GEDCOM 7.0 that aren't in other sample files.

Combined atsign.ged into the existing escapes.ged.

Some files not copied include:

• char*.ged only make sense once there are corresponding 5.5.1 samples in the repository, since all 7.0 files are UTF-8 with a BOM.
• date-dual.ged likewise only makes sense as a 7.0 derivative of a 5.5.1 sample.
• enum-ext.ged likewise looked like it only made sense along with a 5.5.1 sample.
• obsolete.ged and tiny.ged are the same as the existing minimal70.ged.

Addresses part of issue #132