[core/output] Rewrite to hide sys.stout

Add generic "draw()" method that redirects internally to the actual
calls. These can now produce JSON, which is nicer because:

1. Easier to use during testing
2. More flexible
3. Centralizes printing (somewhat)

Still, the "suffix" concept isn't really nice, but so far, I have no
better approach.

core/output.py

@@ -1,18 +1,42 @@
+import sys
 import json
 import time
 
 class i3(object):
+    def __init__(self):
+        self.clear()
+
+    def draw(self, what):
+        data = getattr(self, what)()
+        if 'data' in data:
+            sys.stdout.write(json.dumps(data['data']))
+        if 'suffix' in data:
+            sys.stdout.write(data['suffix'])
+        sys.stdout.write('\n')
+
     def start(self):
-        return '{}\n'.format(json.dumps({ 'version': 1, 'click_events': True }))
+        return {
+            'data': { 'version': 1, 'click_events': True },
+            'suffix': '\n[',
+        }
 
     def stop(self):
-        return ']\n'
+        return { 'suffix': '\n]' }
 
-    def begin_status_line(self):
-        return '['
+    def clear(self):
+        self._statusline = []
 
-    def end_status_line(self):
-        return '],\n'
+    def append(self, module):
+        for widget in module.widgets():
+            self._statusline.append({
+                'full_text': widget.full_text()
+            })
+
+    def statusline(self):
+        return {
+            'data': self._statusline,
+            'suffix': ','
+        }
 
     def wait(self, interval):
         time.sleep(interval)