Update readme and add changelog entry for 1.0.0

Changed

• Breaking: discord-irc now uses tokens for authentication, instead of
  email/password, thanks to @TheDoctorsLife. See the README for more instructions.

0.8.0

Added

• Support for messages containing both attachments and text.

Changed

• Attachment URLs are now posted by themselves, instead of including a
  preliminary message explaining that it's an attachment.

0.6.1

Fixed

• Upgrade dependencies.

0.6.0

Added

• Highlight Discord users when they're mentioned on IRC (thanks to @rce).

0.5.0

Added

• Discord attachments will be linked to on IRC when
  they're posted (fixed by @rce).

0.4.1

[0.4.1] - 2015-12-22

Changed

• Comments are now stripped from JSON configs before they're parsed.
• Upgraded dependencies.