correctly support disabling caps with CAP REQ, fixes #337

Comment out 6668 bindings in default config

These are just used as examples, and prevent Oragono from starting
up if the host doesn't have an IPv6 stack (e.g. inside docker
containers).

See oragono/oragono-docker#5

Add docker info to README

(Here be dragons)

fix spurious bidi violations when casefolding the nickmask of an RTL nick

Mention that the Dockerfile etc are in a different repository

refactor [dk]lines

Even after the timer fired, we were retaining a pointer to it;
clean those up too along with the other cleanup tasks.

two service bug fixes

services refactor

fix #322

some more changes

see https://github.com/ircv3/ircv3-specifications/issues/293

during nick change, removeInternal(client) was being called even before checking
whether the new nick was in use or reserved. Reproduction steps:

1. Log in a client 'alice'
2. Log in a client 'bob'
3. bob issues /nick alice, which fails (correctly) with:
:oragono.test 433 bob alice :Nickname is already in use
4. alice issues /msg bob hi, which fails (incorrectly) with:
:oragono.test 401 alice bob :No such nick

(since it's only accessed from the client's own goroutine)