Turn class WikiQuote into module, add quote and author method, change executable display

First, the existing code was made prettier.  Modules are typically used with libraries, so WikiQuote has been switched from a class to a module.  It still functions just as well as it did before.  WikiQuote.get has been renamed to WikiQuote.quote_of_the_day, but aliases were made for it to be backward-compatible.  Then two methods were added:

`quote`: Returns the quote of the day, prettily formatted in that there is not beginning and trailing garbage.
`author`: Returns the author of the quote.

Also, the executable was switched to printing the quote, then "-#{author}".