Improvements to the hostchange module.

Improvements to the hostchange module.

- Get rid of <host> and merge the prefix and suffix values into the
  <hostchange> value.
- Remove the 'suffix' action. This has been replaced by the 'set'
  action.
- Add the 'addaccount' action. This adds the users account to their
  hostname.
- Use the <hostname:charmap> characters when removing invalid chars
  in addnick mode.
- Allow multiple entries on each hostmask so that they can fall
  through if a certain value is not acceptable.

Closes #816.
Closes #1001.