Update upgrading documentation for 3.1.0 release

Content that should be covered:

• Log file version bump WT-4029
• Compatibility API changes WT-4056 and WT-4098.
• Metadata format change due to saving a timestamp. WT-3905.
• Cursor caching change WT-1228 and WT-3935.
• Table schema operations have different semantics in transactions now. WT-3964.
• wiredtiger_open cache configuration changes. WT-3632.