IRC channel messages are colored green by default
IRC PMs are colored purple by default

* This change avoids 21 deprecation warnings in debug.txt on every server start

2018-05-29 23:46:10: WARNING[Main]: WARNING: minetest.setting_* functions are deprecated.  Use methods on the minetest.settings object.

* Provide backward compatibility by testing for existence of new methods before using them

Fixes #39.

- Use `irc.foo` notation instead of `irc:foo`. It still
  supports the `irc:foo` usage, but will helpfully issue
  a warning with the location of the offending code.
- Remove unused arguments from functions.

As the list command is deprecated, this reference to it should be changed.

Default value is false.

Fixes bug where `Server:  asdf` (note the double space)
gets taken as an empty command name.

Mea culpa. It was possible an error caused `require` to
not be reset, causing possible errors in the future.

Fixes #35.

- Merge `list` into `help`.
- Use `table.concat` to remove trailing comma.

Also minor fixes.

Also minor style fixes.

This allows configuring the mod from the GUI.

Fixes an issue with `hooks.lua` calling the (old, disabled)
`require` function.