Write test for user searching Overheards

First things first, we write a test. Here we're expecting the page to
have:

1. Have an input field labeled `Search`
2. A button labeled `Search Overheards`

Once the `Search Overheards` button is clicked; we're expecting to
*only* see quotes which have the word "Foo" in them.
User may filter overheards

Here we're creating a `filter` hash that tells Datamapper to:

* Sort by id, newest (highest) to oldest (lowest) (i.e. descending)
* Only return overheards with the search terms in their body

When we provide a hash like `{ :body.like => "%some words%" }` to
`Overheard.all` it says:

1. Restrict results based on the `body` field
2. When the body matches our query
3. Our query is 'Anything that contains the phrase "some words"' (`%` is
   the SQL wildcard character)

[Reference](http://datamapper.org/docs/find.html) - Search for
"Conditions"
Add test to ensure API also supports searching

I'm using the
[Enumerable#all?](http://ruby-doc.org/core-2.1.2/Enumerable.html) method
to iterate over every overheard in the response and verify that it
includes the string "Baz".
Update API docs

Gotta tell developers how to use the awesome search feature!
Merge pull request #11 from codeunion/anonymous-user-may-filter-overheards-with-search-query-variable

User may filter overheards with search query variable