See #1698

See #1698 and #1708

PDF forms often use names like "A.1", "A.2", "B.1", "B.2", … for the fields. However, the `.` has a special meaning, so this creates a hierarchy instead.

It was impossible to fill those individual fields with `update_page_form_field_values()`:

```python
update_page_form_field_values({"A": "foo"})  # fills all "A.*" fields
update_page_form_field_values({"1": "foo"})  # fills all "*.1" fields
update_page_form_field_values({"A.1": "foo"})  # fills none of the fields
```

This change makes `update_page_form_field_values()` to also check for qualified field names.

See also: #545

Fixes #1718

in accordance with §2 page 584

Fixes #1710

…1721)

The field /Length is normally required, but Acrobat Reader and other readers are tolerant

Closes #1715

New Features (ENH)
-  Extend PdfWriter.append() to PageObjects (#1704)
-  Support qualified names in update_page_form_field_values (#1695)

Robustness (ROB)
-  Tolerate streams without length field (#1717)
-  Accept DictionaryObject in /D of NamedDestination (#1720)
-  Widths def in cmap calls IndirectObject (#1719)