Makefile for cross-compiling, debuggable elf image

Improved Makefile using a cross compiler toolchaing and dependency
generation.

A linker script for building debuggable ELF files.

Instructions for building a cross compiler and remote debugging with
QEMU and GDB.
Merge pull request #5 from rikusalminen/crosscompile

Makefile for cross-compiling, debuggable elf image