This is a rewrite of the encryption part to support V4 and AES-128 encryption (ONLY decrypt for now)
PyCryptodome was added as an optional dependency for AES.

It does NOT add support for encryption R=6 as introduced by PDF 2.0

Closes #528

Related to #749

All of the following get in [the deprecation process](https://pypdf2.readthedocs.io/en/latest/dev/deprecations.html). This means the old parameters will work for a while to give users a chance to migrate without service disruptions.

`PdfWriter.get_page`: the pageNumber parameter is renamed to page_number

`PyPDF2.filters`:

* For all classes, a parameter rename: decodeParms ➔ decode_parms
* decodeStreamData ➔ decode_stream_data

`PyPDF2.xmp`:

* XmpInformation.rdfRoot ➔ XmpInformation.rdf_root
* XmpInformation.xmp_createDate ➔ XmpInformation.xmp_create_date
* XmpInformation.xmp_creatorTool ➔ XmpInformation.xmp_creator_tool
* XmpInformation.xmp_metadataDate ➔ XmpInformation.xmp_metadata_date
* XmpInformation.xmp_modifyDate ➔ XmpInformation.xmp_modify_date
* XmpInformation.xmpMetadata ➔ XmpInformation.xmp_metadata
* XmpInformation.xmpmm_documentId ➔ XmpInformation.xmpmm_document_id
* XmpInformation.xmpmm_instanceId ➔ XmpInformation.xmpmm_instance_id

`PyPDF2.generic`:

* readHexStringFromStream ➔ read_hex_string_from_stream
* initializeFromDictionary ➔ initialize_from_dictionary
* createStringObject ➔ create_string_object
* TreeObject.hasChildren ➔ TreeObject.has_children
* TreeObject.emptyTree ➔ TreeObject.empty_tree

Fix: Rescan the whole PDF and update/rebuild the trailer

Closes #989

Created a private codecs module

The highlight of this release is improved support for file encryption
(AES-128 and AES-256, R5 only). See #749 for the amazing work of
@exiledkingcc 🎊 Thank you 🤗

Deprecations (DEP):
-  Rename names to be PEP8-compliant (#967)
  - `PdfWriter.get_page`: the pageNumber parameter is renamed to page_number
  - `PyPDF2.filters`:
    * For all classes, a parameter rename: decodeParms ➔ decode_parms
    * decodeStreamData ➔ decode_stream_data
  - `PyPDF2.xmp`:
    * XmpInformation.rdfRoot ➔ XmpInformation.rdf_root
    * XmpInformation.xmp_createDate ➔ XmpInformation.xmp_create_date
    * XmpInformation.xmp_creatorTool ➔ XmpInformation.xmp_creator_tool
    * XmpInformation.xmp_metadataDate ➔ XmpInformation.xmp_metadata_date
    * XmpInformation.xmp_modifyDate ➔ XmpInformation.xmp_modify_date
    * XmpInformation.xmpMetadata ➔ XmpInformation.xmp_metadata
    * XmpInformation.xmpmm_documentId ➔ XmpInformation.xmpmm_document_id
    * XmpInformation.xmpmm_instanceId ➔ XmpInformation.xmpmm_instance_id
  - `PyPDF2.generic`:
    * readHexStringFromStream ➔ read_hex_string_from_stream
    * initializeFromDictionary ➔ initialize_from_dictionary
    * createStringObject ➔ create_string_object
    * TreeObject.hasChildren ➔ TreeObject.has_children
    * TreeObject.emptyTree ➔ TreeObject.empty_tree

New Features (ENH):
-  Add decrypt support for V5 and AES-128, AES-256 (R5 only) (#749)

Robustness (ROB):
-  Fix corrupted (wrongly) linear PDF (#1008)

Maintenance (MAINT):
-  Move PDF_Samples folder into ressources
-  Fix typos (#1007)

Testing (TST):
-  Improve encryption/decryption test (#1009)
-  Add merger test cases with real PDFs (#1006)
-  Add mutmut config

Code Style (STY):
-  Put pure data mappings in separate files (#1005)
-  Make encryption module private, apply pre-commit (#1010)

Full Changelog: 2.2.1...2.3.0