[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/kernel/kernel.module

@@ -0,0 +1,59 @@
+# vim: ft=python
+
+kernel = module("kernel",
+    kind = "exe",
+    default = True,
+    output = "jsix.elf",
+    targets = [ "kernel" ],
+    deps = [ "kutil", "cpu" ],
+    includes = [ "." ],
+    sources = [
+        "apic.cpp",
+        "ap_startup.s",
+        "boot.s",
+        "clock.cpp",
+        "console.cpp",
+        "cpprt.cpp",
+        "cpu.cpp",
+        "debug.cpp",
+        "debug.s",
+        "device_manager.cpp",
+        "frame_allocator.cpp",
+        "gdt.cpp",
+        "gdtidt.s",
+        "hpet.cpp",
+        "idt.cpp",
+        "interrupts.cpp",
+        "interrupts.s",
+        "io.cpp",
+        "log.cpp",
+        "main.cpp",
+        "memory_bootstrap.cpp",
+        "msr.cpp",
+        "objects/channel.cpp",
+        "objects/endpoint.cpp",
+        "objects/kobject.cpp",
+        "objects/thread.cpp",
+        "objects/process.cpp",
+        "objects/system.cpp",
+        "objects/vm_area.cpp",
+        "page_table.cpp",
+        "page_tree.cpp",
+        "pci.cpp",
+        "scheduler.cpp",
+        "serial.cpp",
+        "syscall.cpp",
+        "syscall.s",
+        "syscalls/channel.cpp",
+        "syscalls/endpoint.cpp",
+        "syscalls/object.cpp",
+        "syscalls/process.cpp",
+        "syscalls/system.cpp",
+        "syscalls/thread.cpp",
+        "syscalls/vm_area.cpp",
+        "task.s",
+        "tss.cpp",
+        "vm_space.cpp",
+    ])
+
+kernel.variables['ldflags'] = ["${ldflags}", "-T", "${source_root}/src/kernel/kernel.ld"]