feat: bring back and adapt python bindings with rust core

* import python, try to adapt for rust

* add missing wrapper functions

* - try to write up how to build python bindings
- strike some unused functions from deltachat.h

* adjustments to make tox work

* try to run circle-ci with python build

* don't do docs

* running cargo test as well

* don't run cargo test anymore, that's done in other ci jobs

* also build docs

* don't run doxygen anymore

* subst C with Rust

* a try to get better wheels

Closes #41

python/src/deltachat/props.py

@@ -0,0 +1,30 @@
+"""Helpers for properties."""
+
+
+def with_doc(f):
+    return property(f, None, None, f.__doc__)
+
+
+# copied over unmodified from
+# https://github.com/devpi/devpi/blob/master/common/devpi_common/types.py
+def cached(f):
+    """returns a cached property that is calculated by function f"""
+    def get(self):
+        try:
+            return self._property_cache[f]
+        except AttributeError:
+            self._property_cache = {}
+        except KeyError:
+            pass
+        x = self._property_cache[f] = f(self)
+        return x
+
+    def set(self, val):
+        propcache = self.__dict__.setdefault("_property_cache", {})
+        propcache[f] = val
+
+    def fdel(self):
+        propcache = self.__dict__.setdefault("_property_cache", {})
+        del propcache[f]
+
+    return property(get, set, fdel)