[ADD/WIP] Matrix<->XMPP DMs.

There is still this fun issue with the blocking XML parser leaking
memory on pthread_cancel, I'll try to deal with that later, maybe with a
test stanza.

I also apologise for swearing in the last commit. I promise it won't
happen again, Prosody.

src/XMPPThread.c

@@ -0,0 +1,75 @@
+#include <Parsee.h>
+
+#include <Cytoplasm/Memory.h>
+#include <Cytoplasm/Log.h>
+#include <Cytoplasm/Str.h>
+
+#include <Matrix.h>
+#include <XMPP.h>
+#include <XML.h>
+#include <AS.h>
+
+void *
+ParseeXMPPThread(void *argp)
+{
+    ParseeData *args = argp;
+    XMPPComponent *jabber = args->jabber;
+    XMLElement *stanza = NULL;
+    while (true)
+    {
+        /* TODO: pthread cancelation points */
+        XMLElement *body = NULL;
+        XMLElement *data = NULL;
+        char *to, *room, *from, *from_matrix;
+
+        /* Decoding XML is blocking, which will cause memory issues when we 
+         * want to murder this thread. 
+         * We could ping the server, and die on a "response" stanza, however.
+         */
+        stanza = XMLDecode(jabber->stream, false);
+        if (!stanza)
+        {
+            ASSend(
+                args->config, "!jdHnoKgHCm51ujbw:ari.lt", "_parsee_bridge", 
+                "m.room.message", MatrixCreateNotice("Hi.")
+            );
+            continue;
+        }
+        if (StrEquals(stanza->name, "message"))
+        {
+            size_t i;
+            for (i = 0; i < ArraySize(stanza->children); i++)
+            {
+                XMLElement *child = ArrayGet(stanza->children, i);
+                if (StrEquals(child->name, "body"))
+                {
+                    body = child;
+                    break;
+                }
+            }
+            if (!body)
+            {
+                XMLFreeElement(stanza);
+                continue;
+            }
+            to = ParseeDecodeMXID(HashMapGet(stanza->attrs, "to"));
+            from = HashMapGet(stanza->attrs, "from");
+            from_matrix = ParseeEncodeJID(args->config, from);
+            room = ParseeFindDMRoom(args, to, from);
+            data = ArrayGet(body->children, 0);
+
+            /* TODO: Manage that out. $[to] corresponds to a Matrix 
+             * user, which we need to find the  */
+            ASSend(
+                args->config, room, from_matrix, 
+                "m.room.message", MatrixCreateNotice(data->data)
+            );
+            Free(from_matrix);
+            Free(room);
+            Free(to);
+        }
+        XMLFreeElement(stanza);
+    }
+
+    return NULL;
+}