[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.

src/libraries/cpu/cpu.module

@@ -0,0 +1,8 @@
+# vim: ft=python
+
+module("cpu",
+    kind = "lib",
+    includes = ["include"],
+    sources = [
+        "cpu_id.cpp",
+    ])

src/libraries/cpu/module.toml

@@ -1,4 +0,0 @@
-name = "cpu"
-kind = "lib"
-includes = ["src/libraries/cpu/include"]
-sources = ["cpu_id.cpp"]