Modified assembler to write to .bin file. 

I modified translate.py to work like a real assembler, it reads one filename from the command line, and writes to `file.bin`, where `file` is the basename of the input file with extensions stripped:

```
python translate.py foo.txt
```
the output will be in `foo.bin`.

I also modified the program to output correct logisim bin file header, the resulting file can be loaded directly into the instruction memory on the 16 bit CPU.

Updated the documentation to match.