Further improvements to httphi API (#173)

* add Exchange.WriteBodyString

* Mux.MaxPathValues and other improvements

* Mux PathValue improvemnt and fixes

* MuxSlice more method muxing improvements

* diagram out interesting approach to form parsing for clanker

* refactor RequestParseForm and achieve greatness in API design

* explicit naming of headerCapacityKV value in kvBuffer.Reset

* fix Mux bug not matching paths correctly; httpraw HTTP V1 naming applied

* rename many examples,use httphi in examples,remove useless maxAwaitingConn field

* add ipv4.String

* add ipv4 UnspecifiedAddr and BroadcastAddr

* add ethernet.String

x/xnet/xnet_fuzz_test.go

@@ -21,7 +21,7 @@ func FuzzStackPacketHTTP(f *testing.F) {
 	const seed = 1
 	var buf [ethernet.MaxFrameLength]byte
 	s1, s2, c1, c2 := newTCPStacks(f, seed, MTU)
-	var hdr httpraw.Header
+	var hdr httpraw.HeaderV1
 	err := s1.ListenTCP4(c1, 80)
 	if err != nil {
 		f.Fatal(err)
@@ -129,7 +129,7 @@ func FuzzStackPacketHTTP(f *testing.F) {
 			if n1 == 0 && n2 == 0 {
 				if !closed {
 					if c1.BufferedInput() > 0 {
-						var hdr httpraw.Header
+						var hdr httpraw.HeaderV1
 						n, _ := c1.Read(buf[:])
 						hdr.ReadFromBytes(buf[:n])
 						hdr.TryParse(false)