Documentation change

[Logofile]

This documentation change includes the following:

• Updates the Python tutorial so that examples use Editions instead of proto2, and also removes a section that no longer applies
• In the installation topic, replaces placeholder values in suggested curl commands with actual values
• Adds clarifying content about how values are handled when saving between sint32 and sint64 fields (editions.md, proto2.md, proto3.md topics)
• Adds information about public import commands for Java and its effect on field renaming (proto3.md)
• Corrects information in the textformat-spec.md file
• Adds Rust to the C++-specific guarantees section of cross-version-runtime-guarantee.md
• Updates the version-support.md file for the latest release
• Fixes formatting in Cargo Cult topic
• Adds a news article and a new topic for the upcoming 31.x release
• Updates the encoding and field presence topics to default to editions rather than proto2/proto3
• Adds information to the JSON topic to include information about what happens when numerical data is cast to a smaller type (such as 64-bit data being stored in a 32-bit field)