add state.cache and cache some stuff

oml/cache.py

@@ -0,0 +1,20 @@
+import time
+
+class Cache(dict):
+
+    def __init__(self, ttl=10):
+        self._ttl = ttl
+        self._added = {}
+
+    def get(self, key):
+        if key in self._added:
+            if self._added[key] < time.time():
+                del self._added[key]
+                del self[key]
+                return
+            return dict.__getitem__(self, key)
+
+    def set(self, key, value, ttl=None):
+        ttl = ttl or self._ttl
+        self._added[key] = time.time() + ttl
+        dict.__setitem__(self, key, value)