Native deserialization based on Rust and PyO3

Proof of concept
Only capable of deserializing (nested) Messages with primitive fields
No handling of lists, maps, enums, .. implemented yet
See `example.py` for a working example

example.py

@@ -0,0 +1,22 @@
+# dev tests
+# to be deleted later
+
+import betterproto
+from dataclasses import dataclass
+
+@dataclass
+class Foo(betterproto.Message):
+    x: int = betterproto.int32_field(1)
+    y: float = betterproto.double_field(2)
+
+@dataclass
+class Bar(betterproto.Message):
+    foo1: Foo = betterproto.message_field(1)
+    foo2: Foo = betterproto.message_field(2)
+
+# Serialization has not been changed yet. So nothing unusual here
+buffer = bytes(Bar(foo1 = Foo(1, 2.34), foo2 = Foo(3, 4.56)))
+
+# Native deserialization happening here
+bar = Bar().parse(buffer)
+print(bar)