Parsing Craigslist XML feed

I finally figured out the correct path to use for enums in
RustyXML (the paths inside the crate are different than those
outside the crate confusingly).

I also had to refactor all my static strings to work with
changes to strings in recent Rust versions. Specifically,
I switched ~"string" to "string".to_owned(). This new syntax
is horrible and doesn't play nice with match patterns.

So final result of this commit is that you `make all`, and then
`build/iron-santa` and see a vector of structs printed to the
terminal with the name, description, url, and picture url parsed
from the RSS feed on Craigslist. Hooray!

Unfortunately, there's no price included in the RSS feed. Sometimes
it's in the description, but often not. So, it may be possible to
find prices without doing some crazy scraping of Craigslist.