Allow on-disk files to be read using binary mode 'rb'

[salcock]

The SimpleReader under python3 tends to get unhappy when asked to read a binary file from local disk.

The problem is that these files were always opened using 'r' mode, which means that python3 would treat the contents as utf-8 and try to decode whatever it reads into useful text. When the decoding inevitably fails, python3 would throw an exception.

This PR adds an optional mode argument to the SimpleReader init() method so that the reader can be forced to open the file in binary mode. wandio_open() has also been updated to allow rb as a valid mode, and will pass that on to the Reader init method.

Finally, I've also added a -m option to read_main() (aka pywandio-cat) which allows the mode to be specified via CLI argument.

[salcock]

@digizeph Can you just double-check that I'm not breaking anything else here? -- r remains the default read mode, so in theory it should be OK but it never hurts to have another pair of eyes look over something like this.

[salcock]

Ok, I've just seen the other PR which more or less resolves the same problem.

I think we just need to settle on a solution and get one merged in, as this is starting to cause problems for other users. I think #21 is a better solution than this quick hack, so am happy to go forward with that (and will update my own pywandio using code as appropriate).

[digizeph]

@salcock have you tried out the solution in #21 ? If that works for you then it might be a good choice to move forward. I will double check on my end to see if there is anything outstanding to leave that PR as draft.

[digizeph]

Actually, I have a py3 branch that have fixes similar to what you have here. I think it's worthwhile to try that out.
1a9ba1d
It should handle both binary read and write well.

https://pypi.org/project/pywandio/

[digizeph]

I have implemented the feature in #24 basic local tests work fine.
I also pushed a release of pywandio 0.3.0 to pypi at https://pypi.org/project/pywandio/0.3.0/