Set {trigger: true} as default for history.navigate. Fixes #13

* Changed to `{trigger: true}` by default
* Removed all redundant `{trigger: true}` instances
* Extracted `urlChanged` method to be used within both `navigate` and `checkUrl` methods
* Updated tests (I guess that there's 1 redundant test though which I marked – please verify)
* Updated readme
* All tests pass