[core] Add SASL auth capability

This starts IRCv3 compatibility, but the interfaces should be refined
somewhat.
Merge branch 'master' into ircv3
[docs] Touch up a few flaws in the documentation
[reddit] fix error when poster has been deleted

Fixes #323
Merge branch 'ircv3'
[core] Fix NameError and simplify code.
[core] Remove unblockable from commands in coretasks.

Unblockable was meant for functions that keep track of events.
[rss] Give an error at setup if DB isn't working

This will, at the lease, help diagnose #322
[core] Add bitwise privilege tracking

Includes tracking who is in a channel and IRCv3 multi-prefix support.
I'm leaving #312 open, though, until I'm sure I like the way the API
for the new IRCv3 features works.
[rss] Fix missing import
[adminchannel, clock, radio] Use new channel privileges

Close #326
[docs] Deprecate old-style permissions stuff
[rss] Clean up setup function and RSS feed class

- Rename _RssFeed to RSSFeed
- Generate RSSFeed's attributes dynamically from a list
- Move table creation into its own function
[rss] Update SQL query substitution

- Replaced old-style string formatting with format() function
- SUB no longer needs to be stored in a tuple
[rss] Moved rss actions into their own functions

The .rss command now looks through a list of actions and calls the
corresponding function dynamically.

Also added 'clear' to the help text.
[rss] Moved start/stop commands into main rss command

.startrss is now .rss start
.startrss --stop is not .rss stop
- Removed the debug option; will fix those debug calls next
- Removed a couple other useless variables
- Swapped order of del/clear
- Removed priority import, since they're all in the same function now
[rss] Replace debug messages in read_feeds

- Now uses the built-in debug features exclusively. It's easier to just
have all debug messages go to the same debug_target instead of hacking
together our own half-assed debug system.
[rss] Allow dashes in feed names, add action docstrings, remove clear

- Realized that clear was actually redundant, so removed it
- Proper docstrings on all the rss actions, though there should probably
be a help action as well so they can be accessed from the chat
- Removed priority import, since everything's in one command now
[rss] Create an RSS manager class

Put all the rss functions into a class. This way we don't have to use
global variables like STOP and SUB.
[rss] Added fetch feature to pull all feeds manually.

Will run whether or not regular fetching has been started.