[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.

configs/user-debug.toml

@@ -0,0 +1,34 @@
+extends = "base"
+
+[variables]
+asflags = [
+    "-I${source_root}/src/kernel/",
+]
+
+ccflags = [
+    "-mno-sse",
+    "-fno-omit-frame-pointer",
+    "-g",
+    "-D__ELF__",
+    "-D__JSIX__",
+    "-isystem${source_root}/sysroot/include",
+    "-isystem${source_root}/src/libraries/libc/include",
+    "--sysroot='${source_root}/sysroot'",
+    "-U__linux",
+    "-U__linux__",
+]
+
+cxxflags = [
+    "-fno-exceptions",
+    "-fno-rtti",
+    "-isystem${source_root}/sysroot/include/c++/v1"
+]
+
+ldflags = [
+    "-g",
+    "-Bstatic",
+    "--sysroot='${source_root}/sysroot'",
+    "-L", "${source_root}/sysroot/lib",
+    "-z", "separate-code",
+]
+