Add a scheduler which just keeps of processes for now, and a

with_process to interact with them. User space now has it's own address
space and mapper which means we will be able to allocate memory for it.
I added a bunch of functions as stubs into libxunil which are required
for doomgeneric.

user/libxunil/.cargo/config.toml

@@ -0,0 +1,4 @@
+[unstable]
+    json-target-spec = true
+    build-std-features = ["compiler-builtins-mem"]
+    build-std = ["core", "compiler_builtins", "alloc"]