Multi host URLs, other URL changes (#325)
* adding multi host urls
* linting and more test cases
* tweak unicode_string logic to replace range
* consume leading whitespace on multihost urls
* yet more test cases
* improve coverage
* add vulnerabilties tests
* remove "host_type" from url
* fix unicode positioning with multihost urls
* uprev
* allow default_host, default_port, default_path
* fix schema vs. scheme typo
* empty hosts() if no host
* tweaking url public methods
