Bug fix on create file on render_drawio.

[Maggi-Andrea]

Now we hash the 'filename' node.attributes instead of the keys of the
node.attributes dict.

[modelmat]

What was the bug?
I'll take a look at this is more detail tomorrow night.

[Maggi-Andrea]

I have multipe draw but the extention resolve all of them with the same image, this because when you make the hash with hash_key = "".join(node.attributes).encode() you are performin the hash of the keys in node.attributes and not with their value (node.attributes is a dict). I changed the code to use the 'filename' value from the node.attributes becouse obviously each filename will be different for different directive.

[modelmat]

It might be better to do it off the attributes.values()

One major reason is that currently we have the format attribute which could change between filenames.
If I end up adding width and height this will also change the output file.

[Maggi-Andrea]

I see what do you mean.
I have tried that before to use attributes.values(), but I was getting an exception becouse not all value are jointable into the string, beacuse i.e. some values were list. Obviously this is fixable with a little bit of work.

I selected at first just the filename because this was enouth for me at the moment. Maybe it would be better, insted of just getting all the elements with the values(), get the element we are interested in - ['filename', 'width', ...] - that are responsible for changing the format of the rendered image.

Whatever I think you get the point where the bug is, it up to you selecting the approch you prefer.

[modelmat]

I found a helpful method which will serve our purposes
https://github.com/docutils-mirror/docutils/blob/e88c5fb08d5cdfa8b4ac1020dd6f7177778d5990/docutils/nodes.py#L629-L632

I'm going to close this PR and add it to master.