Cannot decode using CP950 (and possibly others) due to the Python implementation differing from the Microsoft implementation

[TheElementalOfDestruction]

Microsoft's implementation of CP950 has a large portion of the user-defined characters area filled. As these characters are not universal to the encoding, Python's implementation does not accept them when encoding or decoding data, which can lead to encoding issues (this is apparent with RTFDE failing to decode some data using CP950.

A fix is to create the encoding submodule which handles a number of jobs related to encodings, including implementing the Microsoft versions should they be unavailable or differ from the Python implementation.

Version 0.42.0, currently available for preview on the next-release branch, will definitively have support for the plain text body using CP950, as I have implemented code to handle decoding and encoding. If I discover other encodings that differ from the Python implementation, I plan to add them to that release as well and will note them here. Most encodings added will likely only find use on significantly older MSG files, if they find any use at all. However, I decided it would be better to have support for them and not need it rather than not have support and end up needing it.

[TheElementalOfDestruction]

Support for windows-874, one of the codecs that had no support at all, has been added to the next-release branch and as such will be in version 0.42.0. Of course, you may need to verify it's validity, as I cannot confirm test files will decode correctly, however I have implemented it from information I found on it so it should be accurate.

With this I have also adjusted the code to make different types of codecs easier to implement without trying to rely on features that may or may not exist across different Python installs (namely packages that are not listed in the Python documentation at all).

[TheElementalOfDestruction]

Support for the following codecs (using the names that Microsoft uses in its code page map) will also be included:

• x-mac-ce
• x-mac-cyrillic
• x-mac-greek
• x-mac-icelandic
• x-mac-turkish

[TheElementalOfDestruction]

All of the listed encodings have been implemented and should not cause issues. If you are still getting a CP950 error, check to see if it is coming from RTFDE. If it is, you can see the relevant issue here and add that you would like to see support implemented there.