File-Based Cache for NNTP Data

[markrandall]

Enormously improves performance by:

• Lazy-loading the connection to the NNTP server. Now it only makes the connection when the first command is made.
• Using server-side file-based cache

Caches the following:

• Groups and Descriptions for 1 hour - Mainly only needed for the message count.
• Message content indefinitely, including paths of resolved references - These should be completely immutable unless the server is significantly reconfigured.
• Message metadata (descendent messages etc) for 2 minutes - Needed to show new / related posts

Not covered:

• Locking while populating cache key