Reset title/factor to defaults when going back to simple list item

Without this, going from:

    - {url: "http://example.com/rss", factor: 2.0}

to

    - http://example.com/rss

wouldn't reset factor back to 1.
Add a politics feed list
Add tech.txt feed list
Add README.md
Use h2 for sub-headings

Like a civilized person.
Use a deque for the fingerprints

A set is probably more technically appropriate, but I don't want it to
grow indefinitely.
Bump fingerprint limit to 250

Zach Holman's feed includes over 100 entries. I imagine other feeds do
too. I've never seen a feed with more than 200. Hopefully this is enough.
Use a deque for timestamps
Move deque maxlens to class variables
Move request and socket exceptions to global variable
Add a default_update_interval variable

This is used as the update interval when a feed failed to download, it
has no timestamps, or the provided timestamps produced a negative item
interval.

In other words, when things get screwy.
Use __version__
Only hash feed objects on URL
Drop self.item_latest_timestamp
Remove unused instance variables
Update stale docstrings
Catch when a feed is listed more than once

Things get screwy when a feed exists more than once in a feed
list. Catch it before we go any further.
Handle OPML feed lists
Return decoded content from HTTP request

ElementTree can't handle Unicode, apparently.
Skip rss outline nodes without the xmlUrl attribute

Haven't seen this in the wild yet, but no harm in adding the extra
condition.