Add default scheme to Varnish IPs (fix #24)

Rename $ips to $servers and rebuild URL to remove path

Simplify default host handling

This causes the default host to be set on ban requests, too. This shouldn't matter, however, as bans only care about the X-Host header.

Validate Varnish servers
Rename setHost to setBasePath and add validation

Add PHPDoc

Add separate InvalidUrlPartsException

Fix CS and doc issues