Kernel: Pass process arguments directly on the stack.

Get rid of the convoluted get_arguments and get_environment syscalls.
This patch also adds a simple /bin/env that just prints its environment.

Userland/env.cpp

@@ -0,0 +1,9 @@
+#include <unistd.h>
+#include <stdio.h>
+
+int main(int, char**)
+{
+    for (size_t i = 0; environ[i]; ++i)
+        printf("%s\n", environ[i]);
+    return 0;
+}