Add skeleton code unit for argument parsing

Makefile.build

@@ -55,6 +55,7 @@ lib/kernel_SRC += lib/kernel/console.c	# printf(), putchar().
 
 # User process code.
 userprog_SRC  = userprog/process.c	# Process loading.
+userprog_SRC += userprog/parse_arguments.c  # Parses arguments from command line string.
 userprog_SRC += userprog/populate_stack.c  # Populates stack with program arguments.
 userprog_SRC += userprog/pagedir.c	# Page directories.
 userprog_SRC += userprog/exception.c	# User exception handler.

userprog/argument_parsing.h

 #ifndef USERPROG_ARGUMENT_PARSING_H
 #define USERPROG_ARGUMENT_PARSING_H
 
+/*
+ * Given a string containing the command invoking the program `command_line`
+ * and a pointer to an array of C strings (pointer to `char* argv[]`), parse
+ * `command_line` into individual arguments, populate `argv` with these and
+ * return the number of arguments that were parsed (this is the value that can
+ * be used for `argc`).
+ */
+int parse_arguments(const char* command_line, char***argv);
+
 /*
  * Given stack pointer `esp`, argument count `argc` and arguments array `argv`,
  * Populates the stack pointed to by the stack pointer with the given arguments.

userprog/parse_arguments.c

+#include "userprog/argument_parsing.h"
+
+
+int parse_arguments(const char* command_line, char***argv) {
+    #warning "Implement me"
+}