Start X11 and web frontends for xC

For this, we needed a wire protocol.  After surveying available options,
it was decided to implement an XDR-like protocol code generator
in portable AWK.  It now has two backends, per each of:

 - xF, the X11 frontend, is in C, and is meant to be the primary
   user interface in the future.

 - xP, the web frontend, relies on a protocol proxy written in Go,
   and is meant for use on-the-go (no pun intended).

They are very much work-in-progress proofs of concept right now,
and the relay protocol is certain to change.

xP/public/xP.css

@@ -0,0 +1,109 @@
+body {
+	margin: 0;
+	padding: 0;
+	font-family: sans-serif;
+}
+
+.xP {
+	height: 100vh;
+	display: flex;
+	flex-direction: column;
+	overflow: hidden;
+}
+
+.title, .status {
+	background: #f8f8f8;
+	border-bottom: 1px solid #ccc;
+	padding: .05rem .3rem;
+}
+
+.middle {
+	flex: auto;
+	display: flex;
+	flex-direction: row;
+	overflow: hidden;
+}
+
+.list {
+	overflow-y: auto;
+	border-right: 1px solid #ccc;
+	min-width: 10rem;
+}
+.item {
+	padding: .05rem .3rem;
+	cursor: default;
+}
+.item.active {
+	font-weight: bold;
+}
+
+/* Only Firefox currently supports align-content: safe end, thus this. */
+.buffer-container {
+	flex: auto;
+	display: flex;
+	flex-direction: column;
+	overflow: hidden;
+}
+.filler {
+	flex: auto;
+}
+.buffer {
+	display: grid;
+	grid-template-columns: max-content auto;
+	overflow-y: auto;
+}
+
+.date {
+	padding: .3rem;
+	grid-column: span 2;
+	font-weight: bold;
+}
+.time {
+	padding: .1rem .3rem;
+	background: #f8f8f8;
+	color: #bbb;
+	border-right: 1px solid #ccc;
+}
+.mark {
+	padding-right: .3rem;
+	text-align: center;
+	display: inline-block;
+	min-width: 2rem;
+}
+.mark.error {
+	color: red;
+}
+.mark.join {
+	color: green;
+}
+.mark.part {
+	color: red;
+}
+.content {
+	padding: .1rem .3rem;
+	white-space: pre-wrap;
+}
+.content span.b {
+	font-weight: bold;
+}
+.content span.i {
+	font-style: italic;
+}
+.content span.u {
+	text-decoration: underline;
+}
+.content span.s {
+	text-decoration: line-through;
+}
+.content span.m {
+	font-family: monospace;
+}
+
+.status {
+	border-top: 2px solid #fff;
+}
+
+textarea {
+	padding: .05rem .3rem;
+	font-family: inherit;
+}