This was a reference for the params I wanted to support in the
`find_upcoming_events()` method. It's no longer needed.

Instead of doing `use meetup::client::Client`, do `use meetup::Client`.
Makes it less redundant.

This function will format a string containing a date and venue for
inclusion in the description of an RSS `Item`.

Added a `derive(Clone)` on `Venue` in order to be able to clone it to
use its fields in the function.

This allows us to deserialise the venue location for events and include
it in the RSS items.

Now that the `description`, `local_date`, and `local_time` fields are
`Option` types, we need to update the tests to reflect this or they fail
terribly.

I made the change in aa0190279db75f75210f5279afaa62178b242837 but forgot
to update the tests.

After making a request to the API and getting a real JSON response
again, it turns out that the above mentioned fields are actually
optional, and will break Serde's parsing when they're not in the JSON
string coming from Meetup. Make these fields `Option`s so the program
doesn't break when they're not there.

Use 'error-chain' here too. Seems like this will be a pretty useful
library.

Change the include in the 'meetup' `lib.rs` to allow us to export
`meetup::Error` instead of `meetup::errors::Error` to be consistent with
the error types of the other third-party libraries we're using.

Use this instead of `Box`es. Hoping this, along with using the library
in my main crate also, will help me get some more context on my runtime
error.

Hey, it did! Turns out the error is coming from 'serde_json'. Cool.

* Clone the token so we can use it without a borrow error
* Get the response text from our request to the API and try to parse it

This gives me the following panic:

      thread 'main' panicked at 'called `Result::unwrap()` on an `Err`
      value: ErrorImpl { code: Message("invalid type: null, expected a
      sequence"), line: 0, column: 0 }', libcore/result.rs:945:5

Still trying to figure out where my problem is.