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/cutil.py

@@ -0,0 +1,19 @@
+from .capi import lib
+from .capi import ffi
+
+
+def as_dc_charpointer(obj):
+    if obj == ffi.NULL or obj is None:
+        return ffi.NULL
+    if not isinstance(obj, bytes):
+        return obj.encode("utf8")
+    return obj
+
+
+def iter_array(dc_array_t, constructor):
+    for i in range(0, lib.dc_array_get_cnt(dc_array_t)):
+        yield constructor(lib.dc_array_get_id(dc_array_t, i))
+
+
+def from_dc_charpointer(obj):
+    return ffi.string(obj).decode("utf8")