- added information to several docblocks
- changed handling of request headers, added private property for this
- applied changes for improved use of require_once in the README and examples
- added `list_sites()` example
- *potential breaking changes:*
renamed `get_request_type()` and `set_request_type()` functions/methods to `get_request_method()` and `set_request_method()` respectively
- updated README with all getter and setter methods/functions
- updated get_cookies() and get_cookie() for consistency
- get_cookie() remains for backward compatibility only, should not be used in new code
- fix rare cases where the client would end up in a loop, e.g. issuing a request for a site the cached credentials have no
access to
