Graphic state shall store also the font, font size, ...

See #1142

Named destinations are stored in a dictionary in PDF 1.1

Closes #1173

This PR makes sure PyPDF2 uses a consistent nomenclature for the outline:

* **Outline**: A document has exactly one outline (also called "table of contents", in short toc). That outline might be empty.
* **Outline Item**: An element within an outline. This is also called a "bookmark" by some PDF viewers.

This means that some names will be deprecated to ensure consistency:

## PdfReader

* `outlines` ➔ `outline`
* `_build_outline()` ➔ `_build_outline_item()`

## PdfWriter

* Keep `get_outline_root()`
* `add_bookmark_dict()` ➔ `add_outline()` 
* `add_bookmark()` ➔ `add_outline_item()`


## PdfMerger

* `find_bookmark()` ➔ `find_outline_item()`
* `_write_bookmarks()` ➔ `_write_outline()`
* `_write_bookmark_on_page()` ➔ `_write_outline_item_on_page()`
* `_associate_bookmarks_to_pages()` ➔ `_associate_outline_items_to_pages()`
* Keep `_trim_outline()`

## generic.py

* `Bookmark` ➔ `OutlineItem`

Closes #1048
Closes #1098

Closes #1071

* Add AnnotationBuilder.link(...)
* Allow creating a RectangleObject from a RectangleObject. This is useful to create a copy or to ensure we have a RectangleObject with little code.
* Deprecate `writer.add_link` by `writer.add_annotation(AnnotationBuilder.link(...))`.
* Add test for reading an external link annotation.

Closes #284

Replace many os.path usages with pathlib

New Features (ENH):
-  Add ability to add hex encoded colors to outline items (#1186)
-  Add support for pathlib.Path in PdfMerger.merge (#1190)
-  Add link annotation (#1189)
-  Add capability to filter text extraction by orientation  (#1175)

Bug Fixes (BUG):
-  Named Dest in PDF1.1 (#1174)
-  Incomplete Graphic State save/restore (#1172)

Documentation (DOC):
-  Update changelog url in package metadata (#1180)
-  Table extraction (#1179)
-  Mention pyHanko for signing PDF documents (#1178)
-  We now have CMAP support (#1177)

Maintenance (MAINT):
-  Consistant usage of warnings / log messages (#1164)
-  Consistent terminology for outline items (#1156)

Code Style (STY):
-  Apply pre-commit (#1188)

Full Changelog: 2.8.1...2.9.0