[build] Move to python build scripts per module

This change moves Bonnibel from a separate project into the jsix tree,
and alters the project configuration to be jsix-specific. (I stopped
using bonnibel for any other projects, so it's far easier to make it a
custom generator for jsix.) The build system now also uses actual python
code in `*.module` files to configure modules instead of TOML files.
Target configs (boot, kernel-mode, user-mode) now moved to separate TOML
files under `configs/` and can inherit from one another.

scripts/bonnibel/action.py

@@ -0,0 +1,18 @@
+class Action:
+    _action_map = {
+        '.c': Action_c,
+        '.C': Action_cxx,
+        '.cc': Action_cxx,
+        '.cpp': Action_cxx,
+        '.cxx': Action_cxx,
+        '.c++': Action_cxx,
+        '.s': Action_asm,
+        '.S': Action_asm,
+        '.cog': Action_cog,
+    }
+
+    @classmethod
+    def find(cls, ext):
+        return cls._action_map.get(ext)
+
+class Action_c: