chore: set version to a0

Signed-off-by: Daniel Bluhm <dbluhm@pm.me>

Author: dbluhm

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "didcomm-messaging"
-version = "0.1.0"
+version = "0.1.0a0"
 description = "DIDComm Messaging implemented with swappable backends."
 authors = [
     {name = "Daniel Bluhm", email = "dbluhm@pm.me"},
@@ -65,4 +65,4 @@ precision = 2
 show_missing = true
 
 [tool.coverage.run]
-branch = true
+branch = true