Add ability to pipe images into stdin in papirus-draw

[schwma]

Follows Unix philosophy of using output of one program as input to another program.

Allows simple one-liners such as the following:
curl https://raw.githubusercontent.com/PiSupply/PaPiRus/master/bitmaps/papirus-logo.bmp | papirus-draw - -t resize

[tvoverbeek]

Good idea.
We try to have the code Python 3 compatible, since Python 2 will stop to be supported in 2020.
In Python 3 there is a strict separation between strings (text) and bytestreams.
We need a bytestream here for Python 3.
Can you make the code Python 2 and Python 3 compatible?

[schwma]

Hi!
I made my code Python 2 and Python 3 compatible. I'm still new to Python and especially the compatibility problems between different versions, so if there is a better way to handle this, then please let me know.

[tvoverbeek]

@schwma Thanks. Tested it with both Python 2 and 3. Works fine. Merged