Support for IDNA / Punycode Unicode encoding for host names.

Unicode version is natively stored, accessible via `URI.host`, however string and repr will present the IDNA-encoded versions. Tests TBD.

uri/part/host.py

@@ -11,6 +11,11 @@ class HostPart(ProxyPart):
 	def render(self, obj, value):
 		result = super(HostPart, self).render(obj, value)
 
+		try:
+			result.encode('ascii')
+		except UnicodeEncodeError:
+			result = result.encode('idna').decode('ascii')
+
 		if result:
 			try:  # Identify and armour IPv6 address literals.
 				inet_pton(AF_INET6, value)
@@ -20,3 +25,11 @@ def render(self, obj, value):
 				result = '[' + result + ']'
 
 		return result
+
+	def __set__(self, obj, value):
+		if isinstance(value, bytes):
+			value = value.decode('idna')
+		elif value.startswith('xn--'):
+			value = value.encode('ascii').decode('idna')
+
+		super().__set__(obj, value)