fix nomenclature: rename "path" to "url"

@mridgway @redonkulus  @tindli  Finally got time to work on this:
   * We have been allowing `path` to contain query string, and even hash fragment when routr runs on client.  Calling it `path` became very confusing.
   * Also fixed some coding styles for better readability.
   * This is a backward incompatible change.  Will bump minor for the release.
   * Will update flux-router-component and flux-examples as well, after this PR.

Fixes https://github.com/yahoo/routr/issues/10