Add parameterized matching to #displayed?

@samandmoore
Good q.  I think that when you're dealing with URL match comparison, you're expecting to be passing something represented as a string or number.  I only added Numeric casting because I straight up wrote a failing test for this functionality by accident, because numeric identifiers are such a strong part of URLs in common web apps.  Would you be surprised if the following failed?


```ruby
class MyPage < SitePrism::Page
  set_url "/my/path?saucy={saucy_or_not}"
end

...

it "is saucy" do
  visit "http://example.org/my/path/?saucy_or_not=true"
  expect(page).to be_displayed(saucy_or_not: true) #currently would fail
end
```

What about if the URL were `http://example.org/my/path/?saucy_or_not=1`?