Allow spaces in commands and !explain topics.
Merge pull request #12 from andreasots/spaces

Allow spaces in commands and !explain topics.
Don't have !explain fall back to the wiki - it's out of date and not useful
archive.py: open the cache as a binary file

`write' throws an UnicodeEncodeError when it encounters the `ü' in `Adam's Gamehaüs'.
Less spam per Graham request