Feature/hello world kernel land, closes #3 (#4)

* prints hello world

* Builds with the zig build system

build.zig

@@ -0,0 +1,43 @@
+// Zig version: 0.4.0
+
+const Builder = @import("std").build.Builder;
+const builtin = @import("builtin");
+const Array = @import("std").ArrayList;
+
+pub fn build(b: *Builder) void {
+    const kernel_out_dir = "bin/kernel";
+    const kernel_src = "src/kernel/";
+
+    var kernel = b.addExecutable("pluto.elf", kernel_src ++ "kmain.zig");
+    //kernel.addAssemblyFile(kernel_src ++ "start.s");
+
+    kernel.setOutputDir(kernel_out_dir);
+    kernel.setBuildMode(b.standardReleaseOptions());
+    kernel.setTarget(builtin.Arch.i386, builtin.Os.freestanding, builtin.Abi.gnu);
+    kernel.setLinkerScriptPath("link.ld");
+
+    const run_objcopy = b.addSystemCommand([][]const u8 {
+        "objcopy", "-O", "binary", "-S", kernel.getOutputPath(), kernel_out_dir ++ "/pluto.bin",
+    });
+    run_objcopy.step.dependOn(&kernel.step);
+
+    b.default_step.dependOn(&run_objcopy.step);
+
+    const run_qemu = b.addSystemCommand([][]const u8 {
+        "qemu-system-i386",
+        "-display", "curses",
+        "-kernel", kernel.getOutputPath(),
+    });
+
+    const run_qemu_debug = b.addSystemCommand([][]const u8 {
+        "qemu-system-i386",
+        "-display", "curses",
+        "-kernel", kernel.getOutputPath(),
+        "-s", "-S",
+    });
+
+    run_qemu.step.dependOn(&kernel.step);
+    //run_qemu_debug.step.dependOn(&kernel.step);
+
+    b.default_step.dependOn(&run_qemu.step);
+}