Basic native ARM emitter

Resolves issue #800.
It closely resembles the thumb2 emitter, due to the similiarities and is feature-wise on par.
A basic fibonacci snippet
````
def fib(n):
    if n == 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fib(n - 1) + fib(n - 2)

print(fib(30))
````
executes sucessfully, as does tests/micropython/viper.py.
The command line works as well. I haven't implemented a better use of registers > R7, as it was unclear for me what to change.
It's called "ARM Architecture Reference Manual", so that's the official name. With the newer 64bit counterpart, AArch64, it could also be called "AArch32", but there's no reason for it.
Also, shouldn't the thumb2 emitter be called thumb2 emitter instead of "thumb" emitter? It was a bit puzzling to see no mention of thumb2 anywhere yet 32 bit instructions.