Test the machine code generator

[dylanmckay]

in branch avr-obj-support, I have implemented a machine code streamer and an ELF file writer.

Not all instructions are encoded as they should be. We need to compile various programs using avr-llvm to both machine code and assembly. objdump should be ran on the executable to disassemble the program, and then it should be compared with the correct assembler.

Check that the instructions marked untested in AVR_SUPPORT.md are correctly outputted in machine code.

[dylanmckay]

Closing in favor of #26