How to update the mpdecimal source code in this branch:

1. Dowload the new sources in tar.gz format from the mpdecimal download page.

2. Validate the SHA256 checksum of the downloaded file.

3. Unpack the source code and commit the changes:

   # Example with mpdecimal version 4.0.0
   $ git commit -am "Add mpdecimal 4.0.0 sources"

4. Tag the new commit:

   $ git tag -sam "mpdecimal 4.0.0" mpdecimal-4.0.0
   

5. Push changes, including tags, upstream.