[ADD/WIP] Basic XEP-0393 support.

Still needs lots of work. Did I fail to mention I _hate_ HTML?

src/Streams/Writer.c

@@ -0,0 +1,64 @@
+#include <StringStream.h>
+
+#include <Cytoplasm/Memory.h>
+#include <Cytoplasm/Stream.h>
+#include <Cytoplasm/Str.h>
+#include <Cytoplasm/Io.h>
+
+#include <string.h>
+
+static ssize_t
+ReadStreamWriter(void *coop, void *to, size_t n)
+{
+    /* Reading from a stream writer is silly. */
+    return 0;
+}
+static ssize_t
+WriteStreamWriter(void *coop, void *from, size_t n)
+{
+    char **cook = coop;
+    char *tmp = NULL;
+    char *str = Malloc(n + 1);
+
+    memcpy(str, from, n);
+    str[n] = '\0';
+
+    tmp = *cook;
+    *cook = StrConcat(2, *cook, str);
+    Free(tmp);
+    Free(str);
+    return 0;
+}
+static off_t
+SeekStreamWriter(void *coop, off_t mag, int sgn)
+{
+    /* TODO: Seeking would be useful, though not supported yet. */
+    return 0;
+}
+
+static int
+CloseStreamWriter(void *coop)
+{
+    /* Nothing to free as of now. */
+    return 0;
+}
+
+const static IoFunctions Functions = {
+    .read   = ReadStreamWriter,
+    .seek   = SeekStreamWriter,
+    .write  = WriteStreamWriter,
+    .close  = CloseStreamWriter,
+};
+
+Stream *
+StrStreamWriter(char **buffer)
+{
+    Io *raw_io;
+    if (!buffer)
+    {
+        return NULL;
+    }
+
+    raw_io = IoCreate(buffer, Functions);
+    return StreamIo(raw_io);
+}