Items always PAUSED, max connections reached

[decairn]

I see 2 specific problems:

• Max connections (same as issue Max connections reached #16)
• Items always PAUSED and not starting

[decairn]

This should fix both. Has run through several hundred NZBs successfully. Note, AI written. I just needed to get rid of those 2 above problems.

It contains other unrelated changes though:

• Refactored NZB parsing to stream and simplify single-line handling
• Moved queue cooldown wait earlier in socket creation
• Performance improvement of article-success bookkeeping in failure checks
• Updated bottom structure notes/comments

main.py