Encode boolean query parameters as integers

[bakerkretzmar]

This PR changes how we handle query parameters so that boolean values are encoded as integers in the query string. We do this by passing a custom encoder function to qs.stringify() that casts booleans to numbers (and ignores everything else).

Before

route('messages', {
    collector: 1,
    body: true,
});

// 'http://example.com/collector/1/messages?body=true'

After

route('messages', {
    collector: 1,
    body: true,
});

// 'http://example.com/collector/1/messages?body=1'

Motivation

1. Parity with Laravel's route() helper, which also encodes booleans as integers in query strings.
2. Compatibility with Laravel's boolean validation rule, which only recognizes true, false, 0, 1, "0", and "1".

Closes #340.